As I've said in my comments, I think something's wrong with your Windows installation and/or the firmware on your motherboard. You may be able to force the system to boot into its setup utility by unplugging all the disk devices -- hard disks, USB flash drives, optical drives (or at least the discs), etc. When a computer can find no other boot devices, it will normally boot into the firmware setup utility.
If this works, I recommend you try one or both of:
- Reset to defaults -- Sometimes a firmware's settings get damaged in a way that can cause weird behavior. Resetting all the settings to their defaults can usually fix such a problem. There's usually an option to do this somewhere in the setup menus, usually on a screen with options for saving settings and resetting the computer.
- Enable boot-time options -- Various boot options can sometimes disable the sorts of keystrokes you've tried to use. You mentioned one of these ("fast boot"), but there are others, and names can vary. (Sometimes these options describe levels of USB initialization, and setting minimal USB initialization can cause the keyboard to become unresponsive.) If you have another computer (even a smart phone), try Googling option names as you peruse the menus to figure out what they do.
I'm not 100% sure of this, but I suspect that some very early EFI-based x86-64 motherboards might lack the features that Windows uses to produce the "UEFI Firmware Settings" option described by Ƭᴇcʜιᴇ007. If yours is more recent, though (anything made since 2012 or 2013, at a guess), it should have that option when you boot in EFI mode. If it doesn't, that could indicate a bug in Windows or some quirk to the way it was installed. Re-installing might fix the problem, but unless you can track down the cause that may just be pointlessly optimistic.
