I managed to install Ubuntu on my MacBook Pro Mid 2009 but the install was not 100%. I get a - Failed to set MokListRT... message. I've looked it up and others with an old Mac have the same problem. What I want to do now is remove Ubuntu and go back to Mint. I have Mint on USB but I don't know how to get the computer to boot from the USB drive. Ubuntu is the only OS on the computer now. Any hints?