Originally Posted by https://discussions.apple.com/message/12824852#12824852
I have a late 2007 MacBook Pro 3,1. I used to notice lots of odd video related things, like random lines/colors flashing on my external display every now & then for a fraction of a second. Finally, one day in 2009, my laptop screen got jumbled (displayed lots of vertical lines). This would come & go, but was there 90% of the time.
Took it to the Apple store, where they diagnosed a faulty nVidia card. I was out of warranty (didn't have AppleCare), but they replaced the logic board for free.