F12 is not a common key for bios access. I'd double check your motherboard or prebuilt system user manual to verify that it's the correct key for bios access. Usually the bios is accessed via the delete, ESC, F1 or F2 keys. It's possible, but not common. Also, don't hold it down, press it repeatedly as soon as you push power until it accesses the login.
What is your motherboard or prebuilt system model number and I'll verify the procedure.