Try holding the power button down for 20+ seconds - this is shortened in the latest bios update. That should power the machine off. If my memory is correct, f12 is used to select the boot device, f2 is used to enter the bios. I usually hit the f2 key repeatedly on boot until I get to the bios.
Regarding f12, I believe that there is an open issue where the machine will hang with certain bios settings, around quick boot. I’ll see if I can find it and will link it back here if I do.
Update - see the post from RandomUser in this thread:
“In order to use F12 and see the Boot Option Menu, I had to set Quick boot and Quiet boot back to Enabled.”