When I boot I get an error message, something like this:

Power Manager found error, see Power Management

I go into BIOS, go into Power Manager and notice this:

The +3.3v has a +2.94v in red color. Obviously that is the error, but what does it mean? I know it is a power issue, but the mobo manual isn't very helpful.

Is this a mobo problem or powersupply problem, or both?

Please note, this happens at random every few months. Sometimes it gets so bad the computer doesn't want to boot. Other times, like now, I can boot but in the back of my mind I worry about that "2.94v" in red. Turning the computer on / off (power cycling) doesn't appear to help.

What should I do?

Specs:
mobo: p4s800 asus
powersupply: 500w, unable to determine brand, vendor, etc
cpu: p4 @ 2.4 ghz
ram: 1 gb
hdd: 2 IDE each 80 gb
graphics: nvida GeForce FX 5200
sound: no sound card
optical: DVD burner, DVD reader