My computer power on but don't POST

I was checking my email last night and suddenly my pc goes blank and restarted. After the pc restarted it shows power on but it did not post. I had seen inside the cabinet it shows that cpu fan is running, hard drive is working, power supply is also working, but there is no signal on the monitor. I am not able to figure out what happened. Then i started the pc on after a hour later it showing not sign of post. The numlock light is on my keyboard, mouse is working and usb. Recently i had added a video card in my pc. Is the video card affecting my pc. What can be reason for this.

Hi,
Just get relaxed do the following thing. You pc has got this problem may due to overheating.
Change your RAM and reboot your system. Put a different RAM in the place of old one and just check whether your system boots. If this work then probably your RAM is bad.
If not that do you have a another power supply. If yes change your power supply and start your pc. Power supply can be also a reason for your problem.
And on important think if you take out your CPU and place it again be sure that you apply a fresh thermal compound between your CPU and heatsink. Other wise your processor will overheat very quickly.

Remove any CD or DVD if you forget it your DVD drive and restart your computer. Or And second thing i believe this problem is caused due to the your video card. Your resolution is changed which is affecting your display. Remove your display card and reboot your computer. I think it will start working. If no result it might seems that your pc is getting very hot. Change
your cpu fan.

I too got the same problem. The first reason for this problem is overheating and then a bad memory. And then the powersupply. Do one thing before doing the above job.
Remove your power cord and hold the on button on the cpu for 30 seconds or 1 minute. Then connect your cable back and switch it on. If there is no result disconnect all your cables and drives and connect them back.
If nothing happen then dude your mother is gone bad. You have now check out your motherboard or proccessor.

As you said you added a video card in your system. The video card might be the major issue for your problem.
Try the troubleshooting trick to resolve the issue :
Double check that your card is inserted properly in the slot. Some cards are having flaws in their design. Try inserting the card in different slot.
Check out whether the display cable is properly connected to the computer.
Make sue that your monitor and computer is plugged in properly and both are receiving power.
If required, disable any built-in graphics capabilities on your motherboard form your BIOS settings.
And take care that you had selected a proper device when you are installing your new drivers.
Try booting your computer in safe mode.