Bootcamp stuck in Windows
The Mac hardware stores the boot volume in NVRAM so you could power off the computer and then reset things by holding the Command Option P R keys down.

Once you've heard two boot chimes you can release things and if the Mac OS X volume is viable it will boot first. If that doesn't work then it's likely that the OS X volume has issues and the system is failing to boot there and falling back to the second viable OS - Windows.

You might be able to see that in the console if you boot verbose or single user mode.

The official fix at that point would be to boot into Recovery and then see about repairing or reinstalling OS X.


OS X: About OS X Recovery - http://support.apple.com/kb/HT4718