It Works...Then It Don't, Power?

Alright here what up with my main system. At times I turn of my computer it works fine and then the next morning it will not boot up. Not a spin, a hum, nothing. I leave it unplug for a very long time frame like 8 hours or so. Then it works, sometimes. Then it finally happen again left it unplug for 72 hours and still never work. I sent in the motherboard to the makers and they check it out said that the Bios was not that updated. I updated the Bios from the website myself a few months ago, so I can guess that it was not the most up to day bios. So I can say that the motherboard may not have been the issue.

Now for a few months this won't power up didn't happen all the time. It stop and the system worked fine, then it start up again. That some background on the issues.

My question to anybody that reads this is, could the power supply be the main root of the problem? I tested it out and it work fine. The motherboard people said it work fine. I have a video card, DVD drive, three HD in the case but that it. Now sure what could be the problem. There are not system issues I can see from the stats when I check it out. What are your theories on the my problem?

Please fill in your system specs in the user profile area, this will help us ascertain the hardware compatibilities of your system. With out this pertinent information, it makes it very difficult for us here on this forum to help you diagnose your issue(s).

Now that being said, it sure sounds like a dieing PSU from what you are describing. You said you tested the PSU...How? What make, model and wattage is the PSU? Have you made any hardware changes to the system lately?