Replaced graphics card now monitor and keyboard does not work

The usual problem with a completely blank screen, even with known working monitors is the graphics card. Relatively easy to put right with a new graphics card unless the graphics is built into the motherboard. This can be checked by looking on the back of the computer. Is the video outlet grouped with the keyboard, mouse etc sockets or separate from these. If it is with these the graphics card is built into the motherboard and would be uneconomic to do anything with unless the board takes a separate card. If you want to try a separate or different graphics card, make sure you get the correct interface, PCI, AGP, PCIe etc etc

No signal at the monitor indicates (if you know the monitor is working ok) a failure of the graphics chip or graphics card, The lack of indicator light on the num lock LED and the lack of power to the mouse would indicate that there is a major issue with the motherboard.
you can try using another monitor to confirm the problem lies with the graphics, and in the case of the keyboard and mouse, swap them for a usb version, if they work, the Ps2 ports are probably damaged.
I'd be thinking of replacing the motherboard

If it works intermittently then it's either a loose monitor data cable, loose monitor power cable, or loose graphics card. When you say it freezes up, I'm thinking most likely your graphics card is loose, make sure you screw it tight to hold it securely. The power must be off in order to be working with a graphics card. Also ground your body's static electricity to a non-painted piece of steel such as a desk to prevent shocking expensive hardware.

If the motherboard used to work with the old cpu and power supply, but does not with the new cpu and power supply, then probably the cpu or power supply is bad.
Why did you change the cpu and power supply?
If the power supply went bad, it could have overloaded the mother board as well as the old cpu.
If you think the old cpu went bad, how do you know it was not actually the motherboard that went bad?
All I can suggest is that you double check all the connections.
If you have USB mouse and keyboard, try a DIN connected pair.
If you are using the onboard graphics, try a PCI express card instead.
Tell us if there is any front light activity from the power switch, drive, etc.?

"I'm thinking faulty video card, though I'm not entirely sure."

I'm thinking Power Supply.

Bad Power Supply, weak Voltage power rail.

No Signal on the monitor indicates the monitor is working, but the monitor is not receiving a video signal.

1) Could be due to a faulty monitor cable.
When you used the other monitor, did you try another monitor cable, or is this a VGA monitor where the monitor cable is not removable? (CRT monitor)

2) Monitor cable checks out, the next part of the diagnosis would be the graphics card.
Nvidia GeForce 9600GS

1) http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01619745&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&lang=en&product=3867599

It's a Nvidia GeForce 9600 GS 768MB DDR2
One of the weakest graphics cards, (graphics wise), in the GeForce 9600GS series,

http://en.wikipedia.org/wiki/GeForce_9_Series#GeForce_9600_GS_768MB_DDR2

As stated, ensure that the graphics card is seated, down in the PCI Express x16 expansion slot.

[Computer unplugged from power. Observe Anti-Static precautions Before you reach inside the computer.

Anti-Static precautions:

Your body carries Static electricity.
Static WILL fry out (Short Circuit) the hardware components inside a computer.

Computer unplugged from power, computer on a table, computer case open,...TOUCH the metal frame of the open computer case to relieve your body of Static.

Should you walk away in the middle of working on your computer, upon your return Touch the metal frame again ]

After ensuring that the graphics card is well seated, and this is to no avail, I would check to see if the Processor fan is operating.

Computer on, computer case open, observe the Processor fan.
If it isn't spinning, or seems to be spinning very slow, replace the fan.
(Bad fan bearings)

The Pavilion m9515y uses an AMD Phenom X4 9850 processor.
An AMD processor will heat up very quick.
(And typically runs hotter than a comparable Intel)

Without a fan running the Processor could burn up in a matter of seconds.

There is a Fail Safe feature built-in, to shut the Processor off if it becomes too hot.
(BIOS turns it off)

Processor fan is operating okay?
Use the Integrated Graphics on the motherboard, and see if the graphics card is the problem.

The Pavilion Elite m9515y desktop computer has a PCI Express x16 slot, (PCI-Ex16), and also has Integrated Graphics.

(ATI Radeon HD3200, GPU, for Integrated Graphics)

To explain:
The GPU is the 'Graphics Engine'
Graphics Processing Unit.

The GPU chip can be soldered directly to the motherboard, (Integrated Graphics), or soldered to a removable graphics adapter card.

http://en.wikipedia.org/wiki/GPU

(Integrated Graphics is also know as OnBoard Graphics.
On the motherBoard)

When a graphics (adapter) card is used in the PCI Express x16 slot, the Integrated Graphics is not used.

You can remove the graphics card, plug your monitor into the Integrated Graphics on the motherboard, and reset BIOS to use Integrated Graphics, instead of the graphics card.

Graphics on your monitor?
You know you have a bad graphics card.

[Computer unplugged from power, anti-static precautions observed. Remove the graphics card. Plug the monitor into the Integrated Graphics of the motherboard.

{The Integrated Graphics ports are above where the keyboard, and mouse plug in. (Using a keyboard, and mouse that has a PS/2 connector, not a USB connector)

There is a DVI port, (White. Has three rows of 8 holes, and a horizontal slot to the right of the holes),
and a VGA port, (Blue. Three rows of 5 holes)

Plug your monitor cable into the appropriate Integrated Graphics port.

Press the Power On button in, and hold it in for a count of Five seconds. (And I mean at least Five. Count 1001, 1002, 1003, 1004, 1005)

Let go of the Power On button.
Do this procedure two more times.
What you are doing is clearing CMOS Error Codes, and resetting BIOS back to the factory default settings.

Plug the computer into power. WAIT 1 minute.
Turn the computer on ]

After checking out the monitor cable, and Processor fan, I would like you to bypass the graphics card part of the diagnosis, and check the Power Supply instead.

Reasoning?

1) The major cause of computer failure, is Power Supply failure.
Largely attributed to the inside of the computer is dirty, as well as the inside of the Power Supply is dirty.

(The second cause of Power Supply failure, is a low quality Power Supply.
Gauge of wiring is too small.
Electrolytic Capacitors are low quality.
Rectifier Bridge is low quality.
MOSFET's are low quality)

The Power Supply has two cooling components.
The Fan, and Heatsink's used inside.

http://en.wikipedia.org/wiki/Switched-mode_power_supply

Typical construction of a Heatsink is a plate of metal, with tall, thin fins protruding from it.

The plate of metal absorbs heat from whatever object it is placed against, and the tall, thin fins absorb the heat from the metal plate.
The fins radiate the heat away.

If a fan is used in conjunction with a Heatsink, (Such as a Power Supply for example), the air flow from the fan, helps to carry away the heat from the fins.

Once 'Gunk' builds up on the Fan, and the Heatsink/s, the cooling capacity of these two components drops tremendously.

Heat = Wasted Energy
The more heat, the more the Power Supply strains to keep up with the call for power.
Eventually hardware components inside the Power Supply fail, and the Power Supply itself fails.

1) ALL the lights use less than 1 Watt of power.

2) EACH fan uses 2 to 3 Watts.

3) A typical Processor can use from 51 to 125 Watts.
Depends on what Processor it is.

(Pavilion m9515y uses an AMD Phenom X4 - 9850
Operating at full capacity this Processor can use up to 95, or 125 Watts. Depends on which Part Number it is.
HD9850WCJ4BGH or HD9850XAJ4BGH )

This is why if you are seeing lights light up, and fans spinning, (or spin a few times, and stop), the computer itself may not be working.

Not enough power to turn the Processor on.

A computer Power Supply puts out three main voltages.
A) 3.3 Volts (Wires with Orange insulation)
B) 5 Volts (Red wires)
C) 12 Volts (Yellow wires)

Test is done to specifically check the 12 Volt power rail.
11 to 13 Volts is okay.
Less than 11 Volts requires replacing the Power Supply.

The test is done with a multimeter, or a power supply tester.
(An economical multimeter good enough for this test, will run from $5 to $12.
Here is one example of an economical power supply tester,

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5250576&CatId=5471

Need clarification of something I've stated, or have additional questions, please post in a Comment.
(Believe upper right of your page. We are undergoing changes to improve our website)

By the way.

You have one heck of a computer there.

AMD Phenom X4-9850, and 8GB's of DDR2 Sdram ram memory, (PC6400)
With a decent, not too expensive, graphics card, and a decent Power Supply, you could S-M-O-K-E a lot of gamer computers out there.

isolate it first. there are 3 steps: step 1: isolate the monitor. use other monitor. if still no display, step 2: replace video card. if still no display, step 3: replace memory module.

Ha, no kidding!
I just had a HP Pavilion a705w come in for repair at my shop!
Small world.

Okay, let's go with your theory that the power supply is okay, and the Processor is indeed operating.

Your theory is that the GPU on the motherboard isn't working.

No Signal on the monitor means No Video Signal.

The computer isn't sending out a video signal.

(The HP Pavilion a705w comes with Integrated Graphics.

Meaning the GPU is soldered to the motherboard.
Another term for Integrated Graphics is OnBoard graphics.
On the motherBoard.

GPU stands for Graphics Processing Unit.
A GPU can be soldered to the motherboard, {Integrated Graphics}, or soldered to a dedicated graphics adapter card.

http://en.wikipedia.org/wiki/GPU

Do you have a PCI graphics card around? Still have the installation disk also?
Computer unplugged from power, and observing anti-static precautions, plug it in, screw it down to the frame.
Connect the monitor to the graphics card. Plug the computer into power.
WAIT 1 minute. Turn the computer on. You may have bad graphics because you haven't installed the drivers off of the installation CD yet, but you should have graphics.

Don't have a PCI graphics card available, or no graphics showed up on the monitor?

Okay, then humor me for a moment.
Computer unplugged from power. Anti-static precautions implemented.
Take the ram memory module/s out, and clean the gold plated contact pins with a pencil eraser.

Start at the top of the pins, and brush going down towards the bottom.

http://en.wikipedia.org/wiki/File:Generic_DDR_Memory_%28Xytram%29.jpg

Use air to clean off the eraser 'dust', then reinstall the ram.
Plug into power, wait 1 minute, turn the computer on.

Still no?

Have another known, working power supply around, that is an ATX power supply, has at least 250 watts, and has the proper power cables?
I'd like you to use it for a test.

No spare power supply?
Do you have a multimeter?

It's time to check the power out of that power supply.

1) Orange insulated wires are 3.3 Volts
2) Red wires are 5 Volts
3) Yellow wires are 12 Volts
4) ANY Black wire is a Ground wire.

The Positive (Red) lead goes to the power wire, the Negative (Black) lead goes to a Ground wire.
Multimeter is set to the 50 Volt DC scale.

(Auto parts stores sell economically priced multimeter's for around $10 to $15)

Back to your statements in your added comment.

At first it could have been something as simple as the Ethernet card was bad, or the onboard Ethernet was bad.

However, it could be that the motherboard has another issue, and one by one, the motherboards features are going downhill.
No internet. Now no graphics.
Could be this,

http://www.capacitorlab.com/visible-failures/index.htm

I still think the first place to check is the power supply.
It's a cheap quality Bestec power supply.
The Electrolytic Capacitors seem to be the first components that fail in these power supply's.

However, if the computer was dirty inside, as well as the power supply, this could also make a power supply fail.

I've stated what a weak voltage power rail would do. Not enough power to turn the Processor on.
What I haven't stated is that the two main problems with a computer is,

1) The computer is dirty inside, as well as the power supply.
'Kills' power supply's and motherboards.

2) Power supply's are the second item. A pre-built computer manufacturer typically installs a cheap quality power supply.
Saves them money.

Bestec, HiPro, and Delta, are three power supply manufacturers HP uses a lot.
Cheap quality components are used inside.

Believe it or not, if you have a floppy drive in your computer, try unplugging it and disconnecting the data ribbon. Many times, damaged floppy drives can short out motherboard functions and even prevent computers from powering up. If that doesn't fix it, then get a usb keyboard and mouse set (wireless would be fine) or borrow some, and see if they work. If they do, then the power outage damaged the PS2 ports.

use the onboard graphics instead of a seperate graphics card (if installed) to test the screen.if it still doesn't work then unplug your monitor from the mains supply and plug in again to reset it. i doubt it's your monitor that is the problem though. but look on the back of your pc for another connection for your screen. the onboard graphics connection is normally vertical near your ethernet port and mouse and keyboard inputs.

please rate me and give me a fixya! if it helped.

Check the power supply on the PC. Make sure it working. When you first plug in the power to the power supply unit, the fan should "Jump" alittle.