I have replaced the mobo in my dv6000 and still have the same issue. power sometimes comes on for a second or two. Power supply is generic but output is pretty close to spec...within .25 vdc. Should I suspect the processor... or was I sold a bad mobo. Will this post wo a processor? Thanks in advance.

The Gigabyte GTX 470 should be compatible with the Intel DH55TC motherboard if it has a PCIe x16 slot, which is the standard slot for graphics cards. However, there could be various reasons for your PC not turning on, including:
1. Power Supply: The power supply could be inadequate or malfunctioning. Make sure your 600W power supply is sufficient to power both the motherboard and graphics card.
2. Connections: Ensure that all power connections, both on the motherboard and the graphics card, are properly seated.
3. Drivers: Sometimes, improper or outdated drivers can cause issues. Ensure you have the latest graphics card drivers installed.
4. BIOS/UEFI Settings: Check the motherboard's BIOS/UEFI settings to ensure that it's configured to recognize the graphics card and not use onboard graphics (if available).
5. Faulty Hardware: It's possible that the graphics card or motherboard itself is faulty. Testing the components individually in another system may help identify the problematic part.
6. Power Consumption: The GTX 470 can be power-hungry. Ensure that the power supply can deliver enough amperage on the +12V rail for the graphics card.
7. PCIe Slot: Make sure the graphics card is properly seated in the PCIe x16 slot and that there are no physical obstructions.
Given the replacement motherboard also stopped working, it might be worth checking the power supply's quality and output, as it could be a common factor in both motherboard failures. If possible, try the graphics card in another system to see if it functions correctly.

pull out the cpu chip and see if it comes on or beeps,
If it dont its the mobo.

Sometimes the mobo and the cpu go bad at the same time, a bad cpu can kill the mobo

You have suffered a motherboard failure, just to be sure you need to check the voltage at the tip of your AC adapter and leave the system battery out of it, Just try to power it on with the adapter. If the same event happens, you will need to either service the motherboard or replace it. Ebay has several MOBO repair services for the HP products, specifically the DV6000 and the DV9000. These have been HP's problem child for a few years.

You may have a failing motherboard or power supply unit (PSU) then. Just because a mobo has a light on it does not mean that it is getting enough power, just enough to turn that light on. Failure of motherboards and PSU's are usually due to breaking capacitors. A few years ago a capacitor company stole the "recipe" for making capacitors from another company and tried to make their own, unfortunately they did not get the ingredients right and the capacitors started breaking after 2-3 years of use. They sold these capacitors at very cheap prices and a lot of computer companies and power supply makers bought them. This is easy to diagnose. Look for capacitors (caps) (they look like little tiny soda cans) on your motherboard (mobo). They should be perfectly flat on top and not bulged or swelling or leaking anything. There is something in the computer that is not getting enough power and causing it not to start. There are a few companies that will repair broken capacitor issues, if you find that you have that problem. Also if you add a bunch of extra components without upgrading the power supply you can suffer underpowered situations and that can cause internal parts to fail. Have you added any big video cards or extra drives?
And remember a bad PSU does not mean no power, just not enough to run the computer. If you replace the PSU make sure that you replace it with one of the same or greater output watts. Output Watts should be listed on the outside of the PSU itself.
I would try another PSU first if the mobo caps looked good.

It seems like you have bad MOBO. I recently ordered all the stuff to build 2 new systems. Built the first one, no power, just like yours. Moved everything to the 2nd MOBO, everything worked. I did a RMA on the DOA MOBO. Got the new one and it fired right up. Sometimes you just get bad stuff.

Please don't forget to rate this solution.

you have to narrow down the issue.. is it with the pc? or monitor? if you think the cpu... is the power supply fan working? is the cpu overheating? if you think its the monitor...be sure the card is seated properly and check all cables

OK, this can be a hard thing to fix. Most of the time, the power supply is the first thing to go on a PC. However, when you stated that the motherboards LED came on after you unpluged the PS from the motherboard, it leads me to believe that the motherboard is the issue but the power supply might be outputting higher voltages and the motherboard might be shutting down. Since the power supply is cheaper then most motherboards, I would recommend getting a new one. Check ebay for a new power supply. It should be about $20 with shipping. If the same thing happens, then you need a new motherboard...

Check heatsink/fan for CPU first. If this is Ok then try a new power supply.

Sounds like a power supply issue.. Check the mother board for a light when the power is on (some mobos will not have this light). If there is a light, but it does not go on when the power is connected, replace your power supply.

Also, please post the model number of your computer.

Howdy...
I would shed the loads and measure the power supply (pinouts available everywhere on net) what that means is disconnect the drives and I/O cables to them (at the MOBO). Remove any recently added cards or ram . You should be able to see video and/or beeps if voltages are reasonable . A spare power supply would be handy .
Slowly add things until failure shows or if MOBO seems at fault ,try your stuff in another PC . There has been rash of swollen/leaking caps 'round these parts due to bad power supplies or bad caps . Bad power supplies can destroy the MOBO . Changing these caps will often resurect a MOBO 
but this is not for the inexperienced desolderer as these 
boards are multilayer .

Good luck
Hugh I