The normal reason I see a display like this, is if the computer has been dropped and the video cable has jarred loose at the motherboard or underneath the LCD screen.
First step would be following the teardown guide to open up the bottom of the machine and reseat your video connector. Make sure you disconnect the battery before you mess with the cable to keep from having other problems and make sure you pull the cable straight out and not upwards . After you have reseated the cable, reconnect the battery and boot up and see how it looks. Also I am imagine you get the same screen at Bootup. If it looks good at boot up but fails after the system loads, that is most likely your video processor.
I have seen recently a LCD screen after being dropped having the problem also without it being the cable. On that one we had to replace the LCD screen itself. Takes a little time but is fairly straightforward if you follow the guides.