With Windows 8 / 8.1, there might be several possible reasons why you are unable to access the UEFI (BIOS)
- Instead of shutting down, the PC goes into hibernation mode. Upon pressing the power button, the PC doesn't perform a fresh boot procedure, it simply wakes from the hibernation mode. Accessing the UEFI is thus impossible. You can always try to restart your computer in order to gain access to the UEFI.
- If the fast startup mode is enabled, it will be almost impossible to access the UEFI using the keyboard. For more information read:https://ccm.net/faq/31793-windows-8-1-how-to-disable-fast-startup-mode