I was eating breakfast this morning.  Went in to check the weather.  I then went back and finished my breakfast.  Came back in a few minutes later and my computer was off.  I've tried turning it back on, it only runs a few seconds, sometimes makes it to the first boot screen then shuts off again.  Keyboard lights (num lock, etc)stay on.  Would that rule out a bad Power Supply or not?  I built the thing from almost scratch.  It's been flawless for a few years, only recent change in the last probably 6 months or so was a new hard drive that I have Windows on.