My wife has an HP Pavilion 522 Celeron that's about 5 years old. Lately there's been an issue where the screen goes blank in the middle of doing something (or even just at the desktop) , displays "Entering Power Save Mode" and the machine locks up and requires rebooting. I can't seem to find a commonality to the occurances. It's happened while in Internet Explorer, Word, Excel, Outlook or even just at the desktop with nothing open. The only consistant pattern is that it tends to happen within a minute of reaching the desktop after the initial boot in the morning or when it has been off for several hours. On the 2nd re-boot, the system stability may last a little longer, maybe 10 minutes. After that, the increment gets longer. It could be 2 or 3 hours until the next lock up but still random nonetheless. I've tried all sorts of stuff, Spybot, Adaware, SpyDoctor etc. None of them picked up anything. I updated my video drivers thinking it was a video problem. No luck. The motherboard has integrated video onboard. I changed my power scheme settings so the monitor, the hard drive or the system doesn't turn off or go into sleep mode/hibernation. The problem still exists. Would this my a hardware problem or a virus? Any ideas?

Check your Event Viewer log files to see if anything relevant is being recorded. Also check to make sure all your cables are securely plugged in. A loose video or power cable could give you something like this. And does the machine really lock up? Or is it a monitor problem? Try listening to a CD or something and once the monitor goes out, does the music continue to play?