Nothing tagged in Event Viewer. I may have just imagined the screen dimming, because I only thought it happened once. But maybe some more history is in order here. I'm running my old pc-maybe it's 5-7 years old with XP sp3. Until recently I just had an 80 gig hard drive installed, but of course, that was getting full. So installed another 80 gig, and then I had a used 120 that someone gave me. I put the new 80 gig on the same cable as the original 80 gig, and put the 120 on its own cable attached to an i/o controller card. I had a bit of trouble installing the drivers for the controller card, but once that was up and running, all of the drives seemed to be working. That was about a week and a half ago. Now yesterday is when I began having problems with slowing down, freezing, and not completing the boot up or shut down. I tried running my AV in safe mode, but it was going way slower than it should've been and after about 2 hours was only at 16 percent scanned, and that was set on "quick scan". I had also realized that I had not turned off restore points, so I would need to begin that AV scan all over again. I have run ccleaner. I have run malwarebytes which found nothing. My current power supply is 350 watts, which is why I'm thinking that may be the culprit, but I'd like to rule out other things first, before buying a new one.