Can't access BIOS but can boot OS on a asus sabertooth 990fx r2.0

below is pasted a reply I did to another post that might help you: http://www.tomshardware.com/forum/newresponse/2325835

I would remove the battery and have the power cord out. On my new toshiba this forces a date and time entry in the bios.

I am pasting below results of a lot of time spent recently trying to learn about the uefi boot with machines pre-installed with windows 8. I am trying to get this information on a few forums because I drew from a lot of bits and pieces doing the digging I did.
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With windows 8.1 preinstalled on a L55-B Toshiba laptop, to get into bios when the pc is powered off, need to have done a shift+shutdown with windows 8.1 up so does not use fast boot during the next boot.
(can likely accomplish this also by making the permanent changes using the windows 8.1 screens regarding fast boot, I don't know the screen names at this time)
This allows the standard function keys to be active during the boot. That is the old routine of selecting the power button then repeatedley selecting a function key.
Apparently fast boot causes the bios to ignore f2 (get into bios change screens) or f12 (get into boot order screens) during power up.
(or you can shift+restart instead of shift+shutdown to deactivate fast boot to get the function keys to work on next boot)
On this Toshiba, to make bios changes to allow a non uefi boot to work (for instance to boot ubuntu off a usb stick, (non uefi) need to make 2 changes in the bios
(must do in this order on this Toshiba)
1, disable secure boot on one screen.
2, then must change from uefi boot to csm boot on another screen (to use old bios boot)
Then you can boot off a ubuntu usb stick if you change the boot order in the bios permanently or catch the boot using f12 to change the boot order for this 1 time.
I am still not sure how to get into the bios with a broken hard drive if the last shutdown was using fast boot, removing hard drive would likely work?
Maybe booting off something else would allow bios changes on next power up. (like a recovery cd).
I just learned that if my machine has no power to the bios for a few minutes (this Toshiba only has a laptop battery, not a bios and a laptop battery) it will startup up and come to the bios screen right away to have you enter the date and time.