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Hardware: Late 2009 27" iMac (it's the first generation 27")
OS: Mac OSX 10.7, Windows 7 64 bit on Bootcamp

Last night, I decided to upgrade my OS to Yosemite, and seeing how old my Mac OS is (haven't touched it since 2013, I have a MacBook Air that I use as my main machine), I decided to do a fresh install.

Everything went fine for Yosemite, but after that, my Windows stopped working. It's still showing up in the System Preferences.app Startup Disk panel, but not when I hold down the ⌥ Option key during system boot up. However, if I try to boot into Windows from the System Preferences.app Startup Disk panel, Windows will refuse to boot and show an error along lines of

Non-system disk
Press any key to reboot...

What can I do to start up as Windows again?

  • I might be wrong. But i did hear that Yosemite stops supporting Windows and BootCamp. As I said, i might be wrong. You might try to install rEFInd. It might work... – TheBro21 Apr 24 '15 at 7:42
  • @TheBro21 Pretty sure Yosemite supports Bootcamp. rEFInd looks interesting but I'm not sure how well it works with Bootcamp. – jon2512chua Apr 24 '15 at 8:57
  • It works fine. It does display windows properly and the installation is only execute install.sh and then editing the .conf file in the EFI partition – TheBro21 Apr 24 '15 at 8:59
  • Have you tried booting from your Windows 7 install DVD. There is a "Startup Repair" choice on the "System Recovery Options" window. BTW, I just did a upgrade from OS X 10.10.2 to OS X 10.10.3. When trying to boot to Windows 8.1, I received the message "Error loading operating system". – David Anderson Apr 24 '15 at 19:09
  • It would also help if you could give me the "Disk Identifier" for your Boot Camp Windows partition. Open the Disk Utility and highlight (select) the partition, the click on the "Info" button to get the pop up containing the "Disk Identifier". – David Anderson Apr 24 '15 at 21:55
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Found the problem. So it seems that it's a relatively common problem with Yosemite messing up the partition scheme, deleting the header for the Windows partition.

This guy called Loner T had been helping people on the forum, and one of the victims of the bug had written up a summary of the steps to take to fix the issue. Do note however, that the fix is highly technical, and requires at least a competent understanding of operating systems and the CLI to safely apply it. So if you're uncomfortable (or have no idea what the instructions are asking for) it's better to find a professional to help). Obviously it goes without saying that you should have a backup of all your data before you attempt this.

Link to the fix:
https://discussions.apple.com/message/27109000#27109000

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