Nothing happens with the following keyboard shortcuts: it stops at black screen with no forward movement at all and becomes still.
It WILL start into Recovery mode, and Safe boot mode but not OPTION MODE, DIAGNOSTIC MODE, SINGLE-USER MODE. Really weird.
I purchased it as a Refurbished unit off the Apple Site and although the Firmware Password utility shows NO Firmware Password, it behaves
as though there is one. So, in my mind, I wonder if the previous user had indeed set up a FP but I can't see it or denote it.