If I had to make an educated guess I woul say it's the CPU. For the price of CPU's, it's well worth the time/money to bring it to a computer repair shop where they can test a different cpu in your machine.
i dont know much about AMDs but with Intel P4 mobos theres a "p4" power connector, that went out on one at school and had to get a new PSU, if you can try a new psu only if you have that p4