A couple of days ago, my office computer (HP Pavillion 533w) just started shutting down in the middle of whatever I was doing. The screen would go black and the CPU would appear to "hibernate" for lack of a better description. I can still hear it running and it will power down if I press and hold the power button, but it doesn't sound like it's doing anything. This problem has progressively gotten worse, as it used to stay up for 10-15 minutes after bootup and now it won't even get past the inital bootup. I tried a system restore, which it stayed operational for up unitl it restarted and continued it's previous behavior. I've got an inkling that its a hardware problem, but I'm not the most computer literate person. Any ideas??