I have a 2008 Mac Pro Early. I've searched far and wide for this specific problem and posting was my last resort. Before it went dead, sometimes it would randomly crash to a black screen and the video card fan would spin at max speed and I would have to power down. Although annoying, I didn't mind it. Sometimes on a cold power up, it would do the same thing, black screen, a chime, vid fan at max speed, but after a few attempts of powering it off and back on, it would boot up normally. So I figured I'd just have to deal with this to start it up. Now, every time I power up, all I get is a black screen, it STILL chimes, and the vid fan spins at max speed. -I have 4 hard drives installed, 2 OS on separate drives. Both Mountain Lion. -I dusted the whole thing about 6 months ago, and did it again. -I have an ATI 5870 and replaced it with the original NVIDIA 8800, still the fans spin at max speed on startup. -I reseated the ram and riser cards. None of the error lights are on. I tried repositioning all 4 ram sticks, and reduced it to 1, substituted all of them. -I pressed the LED diagnostic button and no error lights. Says it is in Stand by. LED 8 Green: All power rails are functioning, and LED 9 Green: EFI is done loading. -I tried holding CTRL+OPTION+O+F, and CTRL+R, but still nothing. FYI: I used this machine for video editing and has maybe rendered 1000? hours of video, give or take. But in the last year, it has not done anything intensive as video rendering. Occasionally Starcraft 2 at high settings. So my questions are: -does this sound like a bad logic board? -could all 4 of the ram sticks have gone bad? although no error lights. -could it be something as simple as the power supply? -is this thing done? Thanks for reading and I'm sorry if I'm posting in the wrong section or is redundant, my first post. Please help.