Apple has (finally) started a MacBook Pro Repair Extension Program to address video issues on 15″ and 17″ MacBook Pros manufactured in 2011, and 15″ Retina MacBook Pros manufactured between mid 2012 and early 2013.
Symptoms include: Distorted or scrambled video on the built-in display, no video on either built-in or external display although the computer is on, and unexpected restarts.
If you have a MacBook Pro that is exhibiting these symptoms, and falls into the manufacture period, Apple will repair the system free of charge if out of warranty. If you have previously paid Apple for this repair, you are eligible for reimbursement. See http://www.apple.com/support/macbookpro-videoissues for full information.