I have a late 2009 27" iMac with blue vertical lines. I opened it and tried to bake the video card and put it back in but I got a blank screen with the backlight on. I connected my iMac to TV to see if the video card is toast but it showed up okay on my TV screen. I bought a display port cable thinking I broke it and installed it, but it's still showing black screen. Anyone has any idea or suggestion what I should do? Maybe I broke the vertical sync cable?