Ok, I have a custom built pc, about a week ago, my powersupply went out (like the inside blew up, and burnt out) I later replaced the powersupply, and noticed that it would start up, but would shut down automaticly after about 10 seconds. Since then I have replaced the motherboard, CPU and proccessor.

Now, It stays on abit longer then before. but will occasionaly shut off. It was suggested that I try formatting my harddrive. but when i run the setup, it gets to apoint and says starting windows (even though it dosnet have a OS) then just shuts off. I havent done any configuration in the BIOS or anything. The only thing I havent really replaced is the RAM.

Check to see that:

1. The power button doesn't stick down and that you aren't knocking it accidentally.
2. All PSU connections are securely inserted.
3. All hardware is securely in its slots.
4. The CPU is not overheating and that the heatsink is securely attached, and that your thermal compound is properly applied.
5. Your PSU is not underpowered. (check eXtreme Power Supply Calculator Lite v2.5)

Acording the the PSU caculater I only need 480, and I have 550. the power button dosent stick. All conectors, and hardware are firmly connected, and my cpu is not over heating, and my heatsink is securely attached, and my thermal compound is fine.

Go here:

Memtest86.com - Memory Diagnostic

and follow the instructions to run the memory tester. We need to eliminate RAM from this. It would really suck if you had to replace that.