On mine, a 2013 model with detachable keyboard, I have to [re]start, and immediately press the on-screen Windows "Key". This gives me the boot options menu, including F10, etc. There is no on-screen keyboard available. I then have to connect the detachable keyboard (presumably an exernal USB one would also work, but I have not tried), then press F10 (or whatever - there are other options, like F11 for the recovery menu). Just the function key, not the "fn" key then the function key.