Several people here have said that Fast Boot completely disables keyboard interactions early in the boot sequence. This isn't actually true; the keyboard interactions are still ''there'', it's just that, with Fast Boot, the early portion of the boot sequence is so fast that there's almost no time to press the keys to get into the BIOS. You basically have to know the right key ahead of time and start mashing it furiously the moment you press the power button, and even then it'll probably take a few times, but you should eventually manage to hit the key during that split-second window where it'll get you into the BIOS setup.
Proof: I eventually managed to get into the BIOS of my Aspire V5-122P (yes, I know it's a slightly different model of Aspire V5 than the OP's, but Fast Boot works the same on all Windows 8/8.1 machines) using the built-in keyboard (I was trying to get into the BIOS to disable Secure Boot so I could install Ubuntu 16.10 alongside Windows; I didn't know at the time that Ubuntu has supported Secure Boot since 12.10).