SP2 will not turn off digital signature

[ArcticDX]

I have run the normal procedure to make my SP2 turn off requiring digitally signed drivers. However, when I come to the last window (where I am prompted to press 7 or F7), it will not respond. It turns itself off after a while, but if I try to install an unsigned driver, the usual error message comes again. I've tried this with Type Cover, a bluetooth keyboard, and without any keyboard, In fact, the "internal" keyboard will not load at all in this window, so my conclusion is that the SP2 will not respond to any commands in this window. It is fully updated. Any ideas?