Unset boot disk in BIOS, cannot set again

[BluishHumility]

Check that “New Boot Priority” is not set to “Auto”.

Repair of Ubuntu (was: difficulties with install disk)

Oops! On the menu before that one, make sure “New Boot Device Priority” is not set to “auto” and then you should be able to make changes to the boot list. “First” would be the most common choice for this setting.