I have this wonderful Mac Pro that I used for years and about 2 years ago it started making this horrible buzzzzzzzz, and would lock up. After hunting around for a power supply for it, hoping it was a power supply issue, I decided to try a few other things first. Mainly because I wasn't about to pay more then $100 for a used power supply for an old Mac. Mac Pro's like their older siblings the Powermac G5 have quirky symptoms. Sometimes they lock up because RAM is bad, or a controller board on a hard drive is bad. Sometimes its a processor. Sadly Apple diagnostic software and 3rd party software can't always tell you much either. I'm not saying its not a useful tool at times but when Apple diagnostics says all hardware passes tests then why does it lock up? All of the components are not OK. When it goes into a computer coma something is wrong. From experience repairing Mac's I've learned That sometimes you need to swap components to see whats wrong. Well swapping components is all great and fine if you have a vast supply of spare parts that you know are good, and lots of time. But um what if you're an average Joe like me and you don't have gold toilets, and rolls of silk toilet paper in every bathroom of your home? You make judgement calls based on experience. Seems like a power supply, it could be a bad MLB, could be a bad processor, could be RAM. After you're done testing in bare min config and you still haven't solved it what next? We realize I didn't zap the P-ram. Really? Whats that have to do with anything? Well again I've been doing this awhile now and...... after zapping the P-RAM it wont go past 1 reset. Them it ignores my commands and boots. Bad MLB, could be a bad processor, but 95% its bad MLB. Mac pro 1,1 you've been a great workhorse, thank you for all your service. You look like you will make a good bench to sit on now. I'll take you over the hill and put you out of your misery soon.