Computer randomly powers off - Please Help!

[Voland]

Recently, I have left my computer on during the night, downloading things. Next day, the computer was off. THe night after that - same thing happens. Then, I turn on the computer again, leave it for about 30 minutes, come back - and it is again off. I try to turn it on, but it doesnt work. I have to turn the switch at the back of the power supply on and off a couple of times, before I can start my computer. Sometimes it would turn on and turn off before I even got to the BIOS.
So, my question is - WHAT IS GOING ON???
I have a 700 Duron, I was overclocking it to 1 Gig and it was working fine. It still works and boots to Windows, but powers off randomly.
The CPU is not running too hot - never above 40 C. Is it my power supply??? I have 300 W power supply, "Deer" brand. Its probably not the best. but its relatively new - only a couple of months old. Another thing I can think of - I use the Alpha PAL6035 with the Delta fan (7000 RPM). It is suggested to get a 3 to 4 pin cable converter, so that it doesnt draw too much power from the motherboard. Is that a possibility? Anyone have any suggestions?
Thanks a lot in advance.

 

[Santa]

You need an old preist and a young preist..

~~Free Bump~~
No Idea whats wrong..

 

[Fardringle]

First off, it could very well be that your power supply is either just not supplying enough juice, or it's going bad and is not supplying a steady current. Either of these things could cause the system to randomly shut down.

Also, there is a setting in the BIOS where you can have the computer automatically shut down at a certain temperature. Check that and make sure you haven't accidentally set it to an extremely low temperature (about 40 degrees, in your situation) and instead set it to a temperature that actually could be a potential problem - I have mine set to shut down at 60 degrees...