If you have one of these MBP sold between 2011-2013 and are having video issues Apple finally has owned up and will repair out of warrenty, finally!
http://www.apple.com/support/macbookpro-videoissues/
An affected MacBook Pro may display one or more of the following symptoms:
Distorted or scrambled video on the computer screen
No video on the computer screen (or external display) even though the computer is on
Computer restarts unexpectedly
