Sat down to my studios' 2006 Mac Pro the other day and it wouldn't fully boot. It chimes but to a grey screen. Unplugged everything and put it up on the bench went through all the procedures here http://www.macworld.co.uk/how-to/mac/steps-take-when-your-mac-wont-start-3423817/ I reset the video card, 2 usb cards, and the ram cards too still no go. Computer has 5 internal drives total 2 OS, 2 for audio and one for audio samples. Have 2 outboard backup drives. 13 GB ram. Ran utility on both OS drives, there were a few corruptions on the Snow Leopard drive which I fixed the Lion drive seems fine and can do safe mode on both but it's a no go from here thought I'd ask here for other options. I didn't install anything before this happened except Flash player maybe I should uninstall that?