Crashes

Hello,

For a long time now, my computer has been having problems with running for more than an hour or so at a time. After a while, it simply stops displaying anything, but stays on, making noise and having the light still on, but won't respond, with the monitor not displaying anything and not turning back on when I press a key or move the mouse. Occasionally, it will blue screen with something saying BAD_POOL_HEADER or something like that. I'm not very good with this stuff, so I help you guys can help. I've tried restoring, but no luck. Also, when the display suddenly stops, it only turns on again after an hour or so. And if this helps, I recently installed the video card's driver, which was missing, but the problem had been going on long before that.

Thanks in advance.