I was working on an Acer TravelMate that would NOT let me install Windows 8 or Windows 10. Turns out, the SECURE BOOT option was ENABLED and that was the culprit. Unfortunately, the BIOS would not let me select the Secure Boot option to change it. Turns out, there is a VERY easy fix:
Hold down F2 during startup of the laptop to enter the BIOS.
Select menu "Security" using the arrow keys.
Select "Supervisor Password" using the arrow keys.
Press Enter to get the dialog for setting the password.
Type in a password and Enter.
Retype in a password and Enter.
Remember the password somehow! You will be prompted for it the next time you try to enter the BIOS.
Press Enter to dismiss the dialog.
Select "Boot" using the right arrow key.
"Enabled" for "Secure Boot" is no longer greyed out (and can be changed to "Disabled")!
Optional: Set the "Supervisor Password" back to empty.
Select menu "Exit" and menu item "Exit Saving Changes" using the arrow keys. Press Enter for "Yes" in the prompt.
This came from a forum post and I decided to post it here in case that post should disappear: : https://askubuntu.com/a/1001155