I'm not sure if it is just my target machine or if this fast booting causes it, but...

I wanted to reinstall Win8 clean over a Win8 partition and I had one heck of a time banging F2 fast enough to get back into BIOS setup to change the boot sequence. I had changed it before installing the 1st time (and set F12 as "bring up boot menu") but the 1st Win8 install seemed to wipe those settings.

I ended up having to corrupt the boot partition to get in and reset USB CD/DVD as 1st boot device.