Mac Pro starts up but display remains blank

Which graphics card are you using?

I believe i am having the same problems as you are... (using an 8800gt)

Which display are you using? If its a 23" ACD, then it may be a bad power brick on the display. Are you covered by Apple Care? They let me do a DIY repair on the display (which involved swapping the old power brick for a new one they had sent).

I have a Mac Pro, and the 23" Apple Cinema Display. I had problems that made me think it was the card, then the display, but it ended up being the power brick.

I received the Cinema display first (by a few days), and it seemed to work fine - it was hooked up to a Mac Mini. When the Mac Pro arrived I had issues. The Mac Pro would wake up, but the display stayed black. Or the display would turn off spontaneously. I think I remember that unplugging the power cord on the display and waiting 30 seconds, then plugging it back in was one the troubleshooting steps. This is with the Mac Pro on, but no image on the display. ie, you've heard the "ding" but there is not image displayed. This was, IIRC, the confirming bit that the power brick was faulty. If you have the ACD, do a Google search on ACD problems and you'll get some hits. Specifically, try googling the model # on the power brick. I got a different model power brick from Apple Care.

If its not an ACD, then - I'm sorry I can't help. Good Luck

The 23" measurement is diagonally, corner to corner, of viewable display. I don't know if the 20" and 23" models have the same problem. The model number is part of the really really small print on the power adapter (the white brick shaped thing that sits between the wall plug and the display). I think it will start with an "A", but could be wrong about that. I had a heck of a time reading it, and would offer to go read my current one, but its under the desk and I would need to unplug it the whole thing to take it out into a bright room to read. Hopefully we can get you sorted before I need to go to that drastic step!

If unplugging it resets it, then at least you have a work around while the problem is properly diagnosed and fixed.

Are you covered by Apple Care?

Go to the support forums at Apple.com, there is one specifically for ACDs, and do a search for terms like "power button" or "brick" or "Celtron APP 22-611-0344". That last one is the model number of the OLD power brick that was giving me problems.

Anyway, read through these... if you are covered by Apple Care, call them, refer them to this thread (and specifically the posts that talk about a bad brick). Some people claim that this is a known problem (mention that in your conversation). Ask for a Do It Yourself repair. If they accept, then they will ship you a new power adapter, and you will put your old one in the same box and ship it back with a prepaid shipping sticker they provide. Actually, they shipped the the brick and power cord separately - in two different boxes - to me, but Hey - that's efficiency, eh?!

The reason for this as a starting point is that you get to keep your monitor while this is going on. Swapping the brick may not fix it, but its the easiest thing to try. The next step involves hauling the monitor down to the Apple store, where they may or may not be able to duplicate the issue.

Good Luck

In case you conclude that it is not the screen, I am, as mentioned, having similar problems:
Screen remaining black while computer boots. It does however boot properly once in a while which makes it so much more annoying.

I have another posted a thread on my problem:
https://forums.macrumors.com/threads/708376/

I hope it's the display though.