I have been using Boot Camp with Win XP x64 since November successfully on my Mac Pro. Recently I was doing continuous work in an application in Windows, so I set boot camp to boot up using the Windows partition (so I wouldn't need to hit the option key all the time). No problems. When I wanted to switch back to OS X I suddenly couldn't access the boot menu (using the option key), nor boot from CD/DVD ("c"). I am stuck in Windows. Has anyone else had this? Has anyone solved this or something similar?