Right click My computer/Properties/Advanced/Startup and Recovery then click settings. Once there, un check automatically restart. That way, you should get a blue screen with a long code. Write that code down, then google it. That should give you a little more insight as to what may be the culprit.
Also, you might want to go to start/run type in dxdiag. Once there, click the save all information button save the text file to your desktop or wherever you prefer to save it. Then post it's contents here, or email it to support@hitechcreations.com a lot of people have had problems similar to yours and with a look at your dxdiag they may discover something wrong there.
Hope this helps.
P.S. I'm not 100% sure on this, so someone who may know for sure may correct me, but you can pick up a power supply tester for $10 bucks or so. The part I'm not sure on however, is if they only tell you if it *works or of it's dead.
*I don't know if they tell you if it's failing or not, thats where hopefully somebody can correct me.
One last thing, I don't know exactly how computer savvy you are; but if you built your computer or have at least put in more memory/video card etc. If you're not very savvy at all, I'm hesitant to ask you to do this. So, I'll throw a disclaimer that any damage
you may cause while having the side of the case off, is not in any way my fault. I'm giving this information on an as is basis.
Having that said, if you just look at your motherboard (the big thing that everything plugs into *Not trying to be insulting if you know this just covering all bases*) Take a look around and you will find quite a few cylinder shaped things, look at those and see if any of them are bulging or have leaked some yellowish colored substance out. If you happen to run into that, your motherboard will likely need to be replaced. If you have a manufactured computer, contact them if you have any kind of warranty or anything.