Hello there! I have a Mac Pro 3.1 (2008) which won't boot, as you can see in this video: http://www.youtube.com/watch?v=SqCqVUKQy2U These are my tech. specifications: Mac Pro 3.1 from 2008 16 GB RAM 2x 2,8 GHz Quad Core 4 HD's -> 1. Bay -> Crucial 128 GB SSD -> 2. Bay -> Western Digital 2 TB (The MP came with this one) -> 3. Bay -> Seagate 2 TB -> 4. Bay -> Seagate 2 TB (3rd and 4th HD are combined as a RAID) Graphics Card: it could be one of these: NVIDIA GeForce 8800 GT, or NVIDIA Quadro FX 5600 I bought it second hand in december 2012, so there is no warranty. I use the computer for Audio- and Video Postproduction. What I tried: After cleaning it up myself and changing the RAM-Slots, I brought it to an apple-reseller. The guy mentioned, it could be the PSU or logicboard. They took it apart and cleaned it up nicely and afterwards it worked. I came by the shop and he turned it on, no problems. He recommended to buy a new graphics card for performance improvement (f.e. the ATI Radeon HD 5770) though. When I came home it wouldn't boot on my first try. The second time I pushed the button it worked. During working I plugged in an external HD and then it just shut off. The third time I turned it on that evening it worked fine. The next day it wouldn't boot again. The result is, what you can see in the video. Does anybody have a solution? A lot of people on the internet guess, that it could be the PSU or the logicboard. Could it also be the graphics card? Before I'm buying one of these components, I wanted to make sure which one to buy. Especially, because in the shop they couldn't find the problem.... This situation is driving me crazy, especially because I need to work with the mac.