I built my first gaming computer a couple of months ago, this is the parts list:
CPU AMD FX-8350 4.0GHz 8-Core
CPU Cooler Corsair H100 Liquid
Motherboard Asus SABERTOOTH 990FX R2.0 ATX AM3+
Memory G.Skill Ripjaws X Series 8GB (2 x 8GB) DDR3-1333
Storage Western Digital Caviar Black 1TB 3.5" 7200RPM
Video Card MSI Radeon HD 7950 3GB
Case Azza Solano 1000R ATX Full Tower
Power Supply Corsair 600W ATX12V
Optical Drive Lite-On iHAS124-04 DVD/CD Writer
and it worked pretty well. at first it would freeze sometimes (it seemed random, but it froze more often during games). Also it had the strange problem of not turning on when an hdmi cable was plugged in, but a bios update fixed that. the computer still froze but not as often after the bios update (and changing the bios settings to be in high performance mode). I'm still not sure why it was freezing, but now it won't turn on. Those have been the only problems with the computer, i don't think the problems are related to it not starting, but it seems like it's worth mentioning.
Problem is, now my computer only runs for a seconds. When i turn it on, it will start to boot up, it starts normally but turns off after about 20 seconds. if i try to turn it on again it only starts for about 6 seconds, but if i wait a while it will start for longer. Also, i managed to change the bios settings before it turned itself off to power saver mode, now it stays on longer. Because of this i feel like this is a hardware problem, like maybe the power supply or motherboard has a capacitor that burnt out, or maybe the cpu cooler isn't working.
The fact my computer was working (other then the occasional freeze up) for months makes a defective part seem less likely, but i haven't changed any of the wiring or installed any updates so i don't know what else it could be.
One more thing i noticed is the corsair logo above the processor on the cooling unit that usually lights up white turns red and then fades off, then turns red again, sort of like it's a warning that the cpu is getting too hot or something. It seems like some kind of warning but i'm not sure what it means, I don't think it's supposed to do that.
i'm not sure how to troubleshoot this problem though. But i'd like to fix this problem as soon as possible, especially if i have to return a defective part. I bought most of the parts from newegg, i hope there's a warranty...
if the pc has onboard bideo use it and pull the gpu or put in an older gpu that uses less wattage and see if the system stays up. if you dont have any extra parts then start an rma with the power supply vendor. most good ones will do an advance replacment. they send you a new one and you can send the bad one back if it the issue.