My hp pavilion a 1140n turn on fine but my monitor no display pc running good icheck with another monitor and cable but the same monitor no display i dont khow if can be the memory or the mother board monitor out put

Since you have graphics on an external monitor, the problem is the Video Cable, or inside the Display Assembly.

http://h10025.www1.hp.com/ewfrf/wc/product?product=3860431&lc=en&cc=us&dlc=en&lang=en&cc=us

This is a general example of a Video Cable, (Display Cable - HP), for an HP Pavilion DV4 series of Notebook PC,

http://www.ebay.com/itm/NEW-ORIGINAL-HP-PAVILION-DV4-LAPTOP-LCD-VIDEO-CABLE-DC02000IO00-486878-001-14-1-/281038275215?pt=US_Laptop_Screens_LCD_Panels&hash=item416f2fc28f

Mouse over to enlarge

The Video Cable connects to the motherboard in an area under the Keyboard, (About where the Fn key is), routes up along the motherboard, then routes up through the left Hinge, and into the Display Assembly.

From there it connects to the screen Inverter (Display Inverter -HP), and back of LCD screen.
It also connects to the LED backlight.

Either connections are loose, or the Video Cable (Display Cable) is damaged.
If the sheath of the cable shows apparent visual damage, so may be the tiny wires inside. (Stretched/Broken)

Connections CANNOT just be visually determined if they are loose.
You MUST physically check EACH connection.

Tightening connections does no good?
Perform a continuity test with a multimeter set to OHM's, on every wire in that Video Cable.

Have an assistant gently wiggle the cable in the middle, and check for an intermittent reading on the multimeter. Indicates broken wire if intermittent reading shows.

OR,

Take Video Cable to the nearest small computer store, and have the resident tech check it for continuity. Should just be a couple of bucks.

Use an ESD wrist strap, and connect it's alligator clip to a good ground source. (Electro Static Discharge)
Average cost is around $3 to $6.

Here is the download page for the free Service Manual, from HP Support,

http://h10025.www1.hp.com/ewfrf/wc/manualCategory?cc=us&dlc=en&lang=en&lc=en&product=3860431&

Scroll down, click on -
HP Pavilion dv4 Entertainment PC - Maintenance and Service Guide

Page 92 (PDF page at Top) for motherboard side of Video Cable (Display Cable - HP)

Page 80 for LCD screen, and Screen Inverter (Display Inverter - HP), and LED backlight.

Page 82 has false statements.

Remove the display assembly:

1. Locate the wireless antenna cable (1), and remove from path (2)

Should be;
Locate the DISPLAY CABLE (1), and remove from path (2)

2. Disconnect the wireless antenna cable from the system board (3)

Should be;
2. Disconnect the DISPLAY CABLE from the system board (3)

Somebody was on crack that day.

The wireless antenna cable information that follows, is correct.

Video Cable (Display Cable) is on the Left side.
Wireless Antenna wires are on the Right side.

For additional questions please post in a Comment.
Regards,
joecoolvette

Make sure the cable is in good on the back of the computer and on the monitor. If the cables are in good, then either the monitor is bad or the video card is bad. Try using another monitor on the computer. If the other monitor gets a No Signal then the Video Card is bad. If the other monitor shows a display and works, then the original monitor is bad.

Make sure the problem is with monitor (Remove the VGA cable from the PC and check the display of cable check)

you check the RAM, VGA Cable, M/B

Try using a different monitor to check if it is your monitor that is indeed bad.

Also, try using a different cable if possible.

If the computer is at fault (different monitor didn't work either) then you can try installing a graphics card.

Look inside your computer and see if a slot for a graphics card is there. This will be a single unique slot unliek the others in the system.

http://www.ehow.com/video_4445579_gaming-video-cards.html?pid=1&cp=1&wa_vlsrc=continuous&wa_vrid=e626bed1-c9c1-4994-847a-0a9324874691

The video above shows how to choose and install a video card.

I recommend Newegg.com for purchasing

try to switch the blue VGA cable that is connected from the laptop to the external monitor. You may also restart your laptop and set aside the external monitor to check if the laptop is still experiencing garbled display... If it still is, then it is a monitor issue and need to address to HP personnel by calling HP hotline. Otherwise your issue will be resolved by simply doing that..

The issue seems to be due to defective video card on the notebook. Connect and external monitor to the PC and check if it works fine or not. You can follow the steps listed below to connect an external monitor.

1. Turn off the notebook.
2. Connect the monitor cable from the external monitor to the monitor port on the rear/side of the computer.
3. Connect the monitor to a power source and turn it on.
4. Press the Power button to turn on the computer.

At this time, please follow the instructions mentioned below for switching the display to the external monitor:

The notebook's video card supports three modes. Built-in screen only; external video only; and both on simultaneously (mirrored). If you're not seeing the image on the desired device(s), the notebook's video card is probably in another mode. Press FN + F4 to cycle through the display options: Notebook display, External monitor, both.

If you press FN + F4 once, the external monitor will display & there will be no Notebook LCD display.
If you press FN + F4 twice, the external monitor will display & there will be some shading on the Notebook LCD.
If you press FN + F4 thrice, both Notebook LCD & external monitor will display.

If the issue persists on the external monitor, then this could be due to defective video card on the notebook. However, if the display on the external monitor is fine, then the issue is with the LCD display panel of the notebook. In either cases, the notebook requires a detailed onsite diagnosis by a service technician.

If your PC is under warranty, contact HP to get available options to get the notebook repaired under warranty.

Few trouble shoot solution when it comes to these HP Laptop from 08-09.

1). Remove battery and ram. Plug in AC Adapter and insert only ONE RAM into a slot. Boot up and see if this will turn on display (it work on a HP Dv4-1225dx) IF it works then shut down and re insert the two ram and should be good to go :)

2). If your tech savvy remove keyboard and gain access to LCD flex ribbon cable to check if cable is loose (or go on a limb and replace the lcd flex cable ). I would detach it and re attach the ribbon back to motherboard. ( This happen sometimes by chance)

3). Your LCD is shot dead so it will need to be replaced. Current used LCD can range from $40-$50 and new ones with warranty $60-$100. HP is set up for easy LCD removal so shouldn't take more then 30mins to replace, just be careful when handling the ribbon and inverter cables.

GOOD LUCK
(Fix many HP Laptop for friends and family)

Try running a penny across the monitor's cable pins while powered on. If you contact a certain pin with the penny and the monitor exits sleep mode, your monitor is fine. If not, buy another one.

IT could be a motherboard problem with the function key that controls the switching of the video infomation between the LCD screen and the external video connector.
It could be the function key circuitry on the motherboard that controls the back lighting levels on the LCD.

Turn out the room lights and see if have a correct, but real dim, display. If you do, then you have a bad inverter or back light. If you don't, then you have a loose LCD cable connector, bad LCD cable or bad CD.
Ron