I have a 2011 MBP base model 15" and it runs almost constantly with a 23" external monitor connected the following way. ThunderBolt Port --> Apple Mini-Display Port to DVI --> DVI Cable --> Monitor At seemingly completely random times the video will freeze with some garbled appearance to it. Sometimes it won't happen for days...other times multiple times in a day. When it freezes whatever was going on in the background continues to happen but the only way I've found to get things working right again is to force power down then power back on. To see what the garble looks like, check the attached photo. Do you think this is a video card defect?