Previously had Mavericks and recently did a clean install of Yosemite. My Windows installation is not shown in Startup Disk but I can still boot to it by pressing the Option key. Managed to use Windows a few times since installing Yosemite but one day, my Windows 8.1 installation went into BSOD when I tried to open my Mac drive in Windows Explorer. Similar to this error. http://answers.microsoft.com/en-us/...64-using/2e36ca4a-e288-4366-9801-e4ce1587f3d9 My Windows installation disk is from DreamSpark and I made a bootable USB from it using Boot Camp Assistant. This installation doesn't have a Repair your computer option it straight goes to the install screen. There's some GPT MBR error for my BOOTCAMP disk if I attempt to choose that as the drive to install Windows to. I'm thinking it's due some disk partitioning issues? I can still view my Windows files from Yosemite but I can't boot into it!