I have a 15" early-2011 MBP running 10.8.5 that was recently afflicted by Radeongate. I used the workaround to move the ATI* and AMD* extensions to a different folder, and was able to at least log in and backup to an external drive via time machine. I then tried to move the extensions back and try a few other things involving gfxCardStatus, but now, when I boot up (even in single-user mode), I get a "Unable to find driver for this platform: \ "ACPI\" message, and it doesn't boot. I've done some searches and people recommend booting from recovery mode. However, when I do so, the only option is the default "Macintosh HD". My time machine external drive is plugged in, but for some reason, it's not an option in recovery mode. Any help would be appreciated.