G4 freezes on me, changed power supply fan

Hi,
I have G4 that boots up and stays up until I run anything even remotely process intensive (like launch 2 safari instances). After weeks of pondering, the problem seemed to be the fan in the power supply that had quit on me. Now after changing that the problem still continues, any body who has seen this happen. I was thinking of changing the power supply, may be it burned something before the fan was replaced. Is there any place where I could buy the power supply for cheap, I don't want to spend 50-100$ for a new supply. If any of you have one you want to get rid of may be I can buy from you guys.
Anyways thanks for looking and any suggestion is welcome. thanks a ton.
A

TBH...
ebay is your best bet for parts..
I picked up a 64MB Geforce graphics card for £6 inc. delivery for my power mac G4 a couple of days ago....

give it a go...
ebay is like a tresure hunt tho.. the more you look the better stuff and prices you will find...