PC turns itself on and off repeatedly

[sravia]

A new build, but just recently started having this problem. At first, it just took a few on and offs until it turned on completely, now it just turns on and off all the time. The psu apparently works fine, because when I remove the CPU 1 pin (GND I think) the computer turns on again, but nothing happens on the screen.
Tried reseating the CPU, nothin'.

oh, and specs:

OCZ Stealthxstream psu (this ones about 4 years old)
Intel i570
Asus P7P55D
geforce 8800gts 512
Corsair ram

 

[seanc]

Your PSU is getting on a bit, sounds like it has degraded/failing capacitors and cannot power your CPU and graphics card.

With the P4 connector unplugged from the motherboard, you are not powering the CPU, hence the machine doesn't POST and the system will stay on.

 

[sravia]

Okay, I reseated everything a while ago, now my psu doesn't even start. You must be right. Tried hotwiring it, nothing. Oh well, time for a new PSU as well, I guess!