Because Windows 8’s Fast Start, you may not be able to enter BIOS upon initial startup, but if you reboot, it will then be available.
Solutions to enter your Bios:
1. Look in your motherboard manual 🙂
2. Press F2 or Del on your keyboard (two must common keys)
The key should be pressed right after reboot or boot-up, just keep pressing every second until you are inside.