Cannot go back to MacOSX after using BootCamp to start Windows 7 After installing Windows 7 using BootCamp on a 2012 MacPro with HighSierra (Beta). I booted in Windows 7 and now cannot boot back in MacOSX as the BootCamp Utility on Windows isn’t working properly. I’ve tried using the Cmd and Option key combinations to launch in Boot Selector or Recovery Mod, but neither of them work as it seams that the keyboard isn’t being detected until Windows launches. I’ve also tried removing the HDD that Windows is installed on, but that only brings a black screen with a single flashing underscore in the top left corner.

Need urgent support to get back into MacOSX to access my Business Critical applications.
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.