Hello everyone,
 
I am really having problems installing an Evga nVidia gtx680 Mac edition in a mac pro.
Here is the scenario:
 
We have 4 Mac Pros here. I have changed the graphics card in every one of the from the ATI Radeon 5870 to the evga nvidia gtx 680 mac edition.
3 of them work flawlessly without any problems. The last one stalls at the grey boot screen with the Apple logo.
 
All of the Mac Pros are mid 2010 5,1 dual cpu 2.66 GHz with 24 GB RAM running OSX 10.8.4
 
I have tried swapping cards around. The card works fine in another machine.
 
I have tried taking all other expansion cards and unnecessary hard drives out, to see if it could be an issue with the power supply.
 
I have formatted and clean installed the machine straight to OSX 10.8.4.
 
I have tried resetting the PRAM.
 
I have tried holding the power button on startup until the little light flashes.
 
I have tried resetting the SMC by unplugging everything from the computer and holding down the Power button for 10 seconds.
 
Nothing...
 
It just hangs at the grey boot screen with the Apple logo. I can't boot into safe mode (It still just stalls at the boot screen).
 
If I put the original Radeon 5870 card back in the machine it boots fine.
 
I am completely out of ideas. Has anyone of you seen anything similar / have any ideas?
 
Thanks in advance,
Peter

you said you swapped cards around......
did you try a GTX680Mac card from a working machine on the system you are having issue with?

Thanks everyone for answering.
 
@gp-se: I think it is an issue with the Mac Pro as well. I will try and post on Mac Rumors to see if someone there has an idea.
And yes, I did try the card in the second PCI-E slot, same deal. But thanks for the suggestion. 
 
@EVGA_WShelley (& @rjohnson11): Yes I did try another card that was working in one machine on the system with issues. It didn't work either. So I am not really suspecting that anything is wrong with the card itself, more a combo of that particular machine and the cards. So I am more after if anyone has had these issues, or know what could cause them.
 
I know that the machine in question has been used to demo Davinci Resolve some 18 months ago, so at some point it must have had a working nVidia card in it. But what would cause a machine to reject an nVidia GTX680 card but accept a Radeon HD5870?
 
Another note is that if I leave the machine for a period of time at the grey boot screen with the apple logo, it will go into sleep mode. When I try to wake it again, it stalls at the bright blue screen that I see briefly on the other 3 working systems, when waking them from sleep. Before they return to the desktop. (does that make sense?)