PC turns on, off and then on again. Not repeatedly.

[baggedfeet]

Sorry if this is in the wrong section, I'm new here.

My boss's PC turns on for half a second, then immediately shuts off for about four seconds, then turns back on like nothing happened. It stays on and I can do whatever. I've never had a computer do that, is this normal?

Also, I'm not sure if this is caused by the same problem, but the computer randomly shuts off and won't turn back on unless I unplug the PSU from the wall for about ten seconds(or however long it takes for the PC to completely power down).
It happens at random times, I can leave it running for a weekend and it will be on when I come in to work Monday, and sometimes it is on, other times it is off. No power outage, as the computer is the only thing that turns off and I have to proceed to do the step as mentioned above.
Or, I can leave the office for an hour and come back and it has shut off, not all the time, but sometimes.

An old employee built this computer; the specs are:
Gigabyte 970A
AMD FX-6300 Vishera 3.5GHz
8GB RAM
EVGA GT 640 2GB
Barracuda 1TB
Thermaltake 600w
Windows 7 Ultimate

 

[RaDiKaL_]

Sounds like a faulty PSU to me, check it's voltages, if possible change the PSU for a known working one and see if problem disappears.

 

[baggedfeet]

Thanks for the quick reply. That is exactly the problem after checking the voltages.