Only thing i could add to this is to double-check your bios settings against what the manual says, there could be a setting causing this. But i would consider the other suggestions ahead of this one, only thing is that it may be fairly easy to do and indeed you may find the source of the problem.
You have the "caps" suggestion, that makes sense.
You have the power supply suggestion. That one makes a lot of sense as lots of people buy a case for $30 or $40 with a power supply. That makes the power supply a $10 piece of junk that may work for a while but not too long, sorry to say. Same with if you bought a whole computer, unless you specified wanting a good quality power supply.
You can test your existing power supply by getting a digital multimeter, which will do triple duty for the car, house, and computer. You can go to techrepublic, sign on for free, and get their tutorial on how to check your power supply, among other things, great site!
If you do need a power supply i suggest newegg.com as i have seen good ones there for around $42, maybe even less.
I would venture a guess that 20% of all computer problems are a result of a bad or cheap power supply, and i think i am being conservative in my guess. Thats only my opinion, though, not a fact. I can only tell you i have had a lot, A LOT less problems when i decided to only use good power supplies together with a UPS, but the UPS is another story, er, rant.
Good advice + great people = tek-tips