H: Blank screen after powerup
 

I restarted my computer this morning and now all i get is a blank screen.
The mobo screen comes up after i power up, there's a little underscore or dash that flashes in the top left of the screen, and then the screen goes blank (sometimes accompanied by a little flicker).
I can enter the bios and make changes but after that i still get a blank screen. I've tried safe mode and the other modes from the options screen, but all i get is a blank screen afterwards. I've tried booting from my WinXP CD and i still get a blank screen.

I've tried using another videocard but i get the same problem.

It's a pretty old computer, P4P800 ASUS MB, P4 2.8Ghz, ATI 2400HD videocard.

Does anyone have any ideas on what might be the problem?

Try reinstalling the video driver to see if that helps, then
Try reinstalling Windows to see if that helps, then
Junk the computer

reinstall/repair windows? sounds like your bootloader is messed up, as I get the little underscore blinking for a second before it asks me to pick 7 or Vista