I've run out of ideas as to how to fix this problem. I have a late 2009 iMac quad i5, Mountain Lion, 12GB RAM, 1TB HD (recently exchanged under extended warranty).
I stopped counting how many times I have tried to get this up and running but I followed a whole bunch of 'how to's' on the net, including the official Appple guide, but I always end up with a black screen. I insytalled it from scratch using both, Apple drivers on CD and SD card and I can confirn that they installed correctly during my last try. That time I first installed Win Vista, then upgraded to Win 7. I took out the install DVD after first restart and left the SD card in its slot (correctly named, as suggested by Apple). the installation finished, the screen went dark for about 5 min, then the computer rebooted, the screen went dark again for another few min and after that the vomputer restarted again but this time all stayed dark and nothing happened for the better part of an hour.
I also restarted from the Win install disk and tried to remove the ATI drivers using command lines, as suggested in one post.
I need to run Win in Bootcamp because some application I use are very demanding so I need Win to run natively. In an earlier attempt I managed to boot Win7 from the Bootcamp partition in Parallels and I installed the Apple Drivers in that environment but it still resulted in a black screen. I also tried to remove the ATI drivers from Drivers directory manually in MacOS mode but the System wouldn't let me edit the Syustem folder at all, not even in Root user mode.
I understand that I'm not the only one with problem and I feel for you, but please refrain from "me too" posts becuase it doesn't really solve my problem. Thank you.