PC not booting

Hello

I've had this PC that i built myself for around 9 to 10 months. here are the specs first.
775 atx case
power suply 450
HD 200 gb
2Gb ram
MSI motherboard MS7592 Ver 5.2 max 6gb ram.
intel CPU 2.8
It has win XP.

The PC right shuts doewn by itself, it gets to the point when it says starting windows, then it shuts down. I went ahead and swapped out the HD for another HD same thing Shuts down. i even went ahead and took everything out then installed every from scratch. last time i experience this, it was the CPU fan, but this a new fan, everything is new except for the CPU it was used from Ebay. I dont know if replacing it would help, or the same thing might happen.
Any suggestions

 

Check it's stable in bios by hitting del as soon as the computer is turned on,check the health of the computer,cpu temp,system temp,leave in bios for an hour to see if it stays on and keep and eye on the temps,if your seeing hot cpu temps have you used fresh thermal past when reinstalling the cpu?

Did you do a fresh windows install on the new drive? If not windows will most likely not boot so this could be a separate problem causing the second failure.

Will it boot in safe mode? F8 when it's booting.