What were you doing? Seems like you were installing windows.
what happened when you did option+command+r
This is internet recovery. It will take awhile. takes 15 minutes to boot on my 5meg connection.
What a happens when you ...
Boot to Startup Manager
Power off your machine. Hold down the option/alt key. Power on your machine. Continue holding down the option/alt key until you see an icon. Click on the start drive you wish to boot. Click on the right arrow icon or press the return key.