This is actually because of a BIOS setting. Start the computer and press F2.
Navigate to Advanced
Go down to System Configuration and press enter
You will see something called Boot Mode. It is probably set to UEFI Boot. Select and Press Enter.
Choose CSM Boot.
Press ESC and then Exit with saving changes. You computer should now boot again from the Disc/USB.
When done you must set it back to UEFI or Windows 8 will not boot.