[Cottonsworth]

I purchased an used, Apple refurbed Early-2008 Mac Pro (8-Core 2.8ghz x 2, ATi 2600XT, 2GB ram basically completely stock) and Snow Leopard. It is currently out of warranty. At the time of purchase the previous owner told me that the computer wouldn't start and that a power supply replacement would remedy that. After getting the computer I took it to the Apple Store and viola, it turned on fine. It seemed to work fine for a few days but then had trouble starting.

Here are the symptoms:

-The computer powers on, the video card fan turn on and it would reach the Apple logo with the spinning thing below the logo and then shut off. OR
-The computer powers on, the video card fan turns on and then the machine shuts off before the monitor comes on.

-If I leave the computer completely unplugged for a couple of days, it does boot fine and reach the desktop. I'm able to maybe work for a few minutes (sometimes it does go for a few hours) before the machine shuts off without warning. Oddly, this seems to only happen if the computer is off for a few days, leaving it off for a few hours doesn't seem to do the trick.

I have already tried resetting the SMC and removing the memory and video card and putting it back in both the original and different slots. While the computer was able to stay on, I did run disk utility and the hard drive checks out ok.

I tried reading different threads on this issue and it seems like it is one or a combination of the following scenarios:

1. Bad logic board
2. Bad power supply
3. Bad video card
4. Bad hard drive

Based on my symptoms, can anyone offer me some knowledge and advice on what the issue may exactly be? If it is a bad power supply, would it even come on occasionally, etc etc. Thanks in advance for any help.

[P]

Power supply is highly likely. Mobo is an outside possibility.

[Big Mac]

There's no reason not to think it's the power supply. The original owner even said it was faulty, right? With power problems you always suspect the power supply as the primary suspect.

[Cottonsworth]

Yes, I thought it would likely be the power supply but after doing a few internet searches it seems like a lot people that have general shutdown issues had to have the logic board/video card replaced but everyone's shutdown issues seem to be a bit different, so I was hoping a detailed description of my problems might yield a better analysis. I'm just worried that I'll have to replace too many components to the point of just buying a new machine. :/

Would you guys suggest having the Apple Store replace the power supply or should I just purchase one off the bay? Thanks again.

[Athens]

You can visual inspect all the capacitors on the motherboard to see if any are leaking. IF any are, that points to a motherboard problem.



Its to dangerous to inspect the power supply. NEVER open that up because it maintains a charge even if off. Can kill you. I would pick up a used power supply to save money. My bet is going to be the power supply like the others said. I can safely say it wont be your hard drive, and its pretty rare for a video card to cause power cut off problem. Normally bad video cards result in no video or garbage video. Motherboard, and Power Supply usally result in sudden turn offs. Bad Ram usually results in reboots or start up crashes.

[Waragainstsleep]

Closest symptom match in the service manual says to check the diagnostic LEDs on the logic board. It also says to reseat the CPUs, replace the CPUs, replace the logic boards and replace the PSU. In that order.

I actually think the video card might be a good bet. Next time you get it running, as well as checking the LEDs turn on screen sharing and then try running it without a video card at all. Just share the screen periodically to check its still running. Or just try this anyway, if it doesn't power off with the GPU removed, its probably the graphics card.

I might have a Radeon 5770 available for sale soon. I'll post it in the marketplace when I get my hands on it but if you (or anyone else) is interested, PM me.

Despite all this, Apple will more than likely diagnose the fault for free though Mac Pros can be absolute b*****ds to diagnose properly. I'm not sure I'd trust them, you might end up paying a lot for an unnecessary or incorrect fix. They don't go wrong very often but they tend to fail in either complex, obscure or spectacular ways when they do.