27” Apple iMac, Windows 7 installation and a blank screen

I recently picked up one of the new 27” iMacs with ATI Radeon 4850 graphics and so far I’m impressed. It’s a smart piece of hardware.

Out of necessity I need be able to boot into Windows 7 so I decided to install it (64-bit build) via Boot Camp. The first phase of setup proceeded without incident but at the point where Windows Setup loads the display driver, the screen went blank. It seems the ATI driver on the Win 7 RTM DVD doesn’t play nice with the ATI Radeon 4850 video in this particular iMac…

Fortunately, Setup doesn’t prompt for user input before rebooting …

To continue with Setup (or at least to be able to see anything on the screen) you need to intervene at this point and disable the ATI driver, here’s one way:

  • When prompted, hit any key to boot Windows Setup from the CD.
  • Select a Language, etc. and then click “Repair your computer”.
  • Select the Win 7 OS that you’re in the process of installing and click Next.
  • Start a Command Prompt and run regedit.
  • Highlight HKEY_LOCAL_MACHINE and then select File –> Load Hive…
  • Load the System hive from C:\Windows\System32\config\SYSTEM under say, “SystemHive”.
  • Locate the ATI driver (atikmdag) under SystemHive\ControlSetnnn\services and set Start to 4 (disabled). Here, nnn corresponds to the value at SystemHive\Select\Current.
  • Unload the hive, close regedit and reboot.

You should now be able to continue successfully with the remainder of Setup.

Once booted into Win 7, Windows Update will download the latest ATI driver which appears to work well and supports the native resolution of 2560 x 1440.

Now you can proceed as normal and install Boot Camp. Once done, you should have a fully functioning dual-boot 27” iMac!


  1. Justin said,

    January 2, 2010 @ 6:58 am

    Thanks for the info, this helped me complete my Win 7 Prof x64 install on Boot Camp.

    Have you had anyone report problems in Windows with graphics drivers after the install was successful? When using Windows, I get frozen screens, yellow / pink polka-dots, and sometimes a black frozen screen.

    Often times after this happens my desktop background goes from pictures to a black screen.

  2. David said,

    January 5, 2010 @ 5:46 am

    I haven’t noticed any issues so far. I’m running version 8.661.0.0 of the ATI driver.

  3. Josiah LaChance said,

    January 15, 2010 @ 6:36 pm

    Hey Man, I just purchased my new iMac & W7 and ran into this same problem, if anyone else has this problem, HERE IS THIS FIX!!!

    Thank you David!

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