Chosen Solution
I´ve read hours worth of forum posts regarding this and similar issues with the display but still not sure how to proceed. It shows 5 vertical stribes immediately and after Apple logo it stalls at a white/grey screen. Can boot in safe mode - stribes still there and depending on the background they can appear green and other colors. Screenshot does NOT show stribes! External display WILL show stribes. iMac used as a display - NO errors on screen. Those green diagnose led lamps (through vent holes) seems to turn on all 4 of them even though I´m having a hard time being 100% sure of the no 4 led. Boot from a clean 10.10.2 external HD makes no difference to the above mentioned. Have pulled out the graphics card and sav a little smudge on the connector pin - cleaned it (with clean air) and reaseambled. Still same problem. I where preparing my self to put my graphics card in the oven or buy a new/replacement one but I´m not sure that it is with the graphics card alone or something else might be causing this. I´m understanding it as my screen shoot should show the error stribes as well, should this be a graphics card failure. Any suggestions?
What you’ve described indicates a bad graphics board. On these models the video RAM is on the graphics board not shared with the system RAM. Glitches from a graphics card will not show up in a screen shot. You can try the oven fix as a last ditch effort, but that would only fix it if it is a solder joint issue.
