Hi, I've read the threads and can't seem to find anything unique to my problem. I really need some help as the searches out there in google don't help. I have a Mac Pro Quad Core 2.8GHz and it was working fine until a few months ago. First it was turning off at unexpected times. I'd put it to sleep and even find it had shut down by itself after standing there to watch to make sure it went in sleep mode. So I took the whole thing apart, reset the PRAM and everything that I could do to try and fix it. Cleared the memory cache (or something like that). Even took the front and rear fans out to clean the dust out of it. After that when I initially started it up again, it would start up for about 1-2 seconds then turn off. I pressed it quite a number of times and it eventually booted into Snow Leopard OS (by the way, I even reinstalled all my software thinking it might be a software issue). So I got scared and backed everything up. But for the next two weeks it worked perfectly fine EXCEPT that I couldn't put it in sleep mode anymore. When I did that, it would shut down immediately. But I didn't care since I was happy that I could leave my Mac Pro on again the whole day. Well, 2 weeks later, and one day it just decided to not turn on again anymore. It would boot up and shut down after 2-3 seconds and after about 20 more times of trying, it booted up, and I was able to back up all my work again and after that I immediately turned it off. Please help! I really like this machine but it just has been so weird lately. I've turned it off and haven't used it since then. I've had to use Photoshop and Lightroom on my macbook air 11 inch which is HORRIBLE!