Cannot go back to MacOSX after using BootCamp to start Windows 7
Try something for me, if it doesn't work, ask someone else.
Restart the computer.  Right after you hit the restart button, press and hold the option key until it either boots into one of your operating systems or pops up a screen in which you can switch between the two.  That's how I had to switch between windows and MacOSX on my mac.