For some time now I have struggled with getting the proprietory nVidia drivers to work on a system with UEFI Secure Boot enabled. What would happen is the drivers install correctly but do not load due to Secure Boot signing verification mechanism does not complete successfully. Reading suggests that mokutil --import MOK.der should load the key to the Secure Boot database ready for the enrolment process to complete upon reboot. This enrolment process should present a screen where the certificate password is requested.