Here's a situation, I recently had to wipe my hard drive, due to a virus that I could not get rid of, after loading my programs however I now have an unusual problem.  Now, if I'm working everything is fine, but if I let the computer sit for 15-20 minutes the screen goes blank and it fails to recognize both the mouse and keyboard, and the power light flutters.  Thinking it was the power supply I replaced that but still have the same problem, anyone have any ideas??

  Is it hibernating?  I would check the Power Options in the Control Panel and make sure one of those settings is not causing your problem.