USB compatibility mode off = can't enter BIOS

I've got a Z77 Extreme 4. Had some problems using the USB keyboard while the computer was starting (the keyboard would stop working just before Windows asked if I wanted to abort CHKDSK...), so I thought I'd try turning off the USB compatibility mode. I've done that before on previous boards from other brands, and so I expected to be able to get back into the BIOS even with this mode off (and without trying to find a PS/2 keyboard... come on, they stopped making those decades ago. Keyboards since 2010 (such as mine) won't even work with a PS/2 adapter!).

It didn't work, I still couldn't use my keyboard, but worse yet, I can't even enter the BIOS. I can't change the boot device or do anything else. WHAT. THE. HELL?! What was ASRock thinking?

Is there any way to access the BIOS? I know I can reset it, but I really don't want to, because all my settings would be lost. I spent a long time tweaking them, and wouldn't be able to reconstruct them, and I certainly don't have the time or will to tweak around again.

This is lunacy, especially considering that people may have a really good reason to deactivate the compatibility mode... it can cause quite some problems. You can't expect those people to have a spare PS/2 keyboard somewhere...