I just built a new Desktop PC. It was supposed to be for me to do simple tasks for my computer. Here are my specs.

PSU is 450WATTS and its an ATX that came with the case

Intel Celeron D 2.66 GHz Processor

MSI PM8M3-V Motherboard
w/ 3 PCI slots
1 AGP Slot

Maxtor 320Gb SATI Harddrive

and 2 RAM's
256mb
& 512mb.

Well I installed everything correclty rechecked and everything was fine there. I had everything installed correctly and My Computer Does power up and seems to run fine. Then within 5-60 seconds the computer turns off voluntarily. All the RAM has been tested. Switched slots.blah blah. Nothing works. All forums in witch i've looked at give no solutions. The only thing i havent tried is switching the power supply. If anyone knows anything to help that would be greatly appreciated.ahhhhhh.