Georg, I've read that the vertical lines have something to do with the display card not working. My Dh's computer has the same problem and I'm searching the internet to see if there is anyway to be able to replace it. So far I haven't found anything helpful or significant. I don't think it's fixable w/o you having to take it to an Apple store. Probably done like that on purpose. If I were able to find a way to be able to fix it, I know I could probably do it, since I've replaced the hard drive on one of my older iMac's. -Katia