Bootcamp interrupted; now stuck on Windows boot looking for startup I have a MBP with Yosemite (10.10.5 I think). I was trying to install Windows 7 from a USB and cancelled it when it got stuck looking for a driver - I don't have any disk drive and that seemed to confuse it; there didn't seem to be an option to go back or cancel so I think I just powered down by holding down the power button.

Now when I try to startup it seems to be stuck in Windows mode looking for a bootable device.

Is there a key combination that will make it reset back to starting in Mac OS?
To bring up the Startup Manager, press and hold the option key immediately after you turn on your Mac and hear the startup sound.

For additional information see: Startup key combinations for Mac and How to choose a startup disk on your Mac.