iMac blank grey screen

I was playing some Kerbal Space Program and out of nowhere my Mac kind of just stopped and showed these pixel squares and froze, so I turned it off and rebooted and everything was fine so I rebooted the game and it did the same thing. Now when I boot up it shows the apple logo all grainy and it goes to this just blank grey screen then eventually to a checkerboard pixel mess. It runs in safe mod but with these pixel lines running thru it. Is there anything I can do? Apple told me it was either Graphics card or hardware error.

The fact that you are seeing a pixel mess when outside of the space game leads me to think that the Apple guys are right. Which Mac do you have. In many of the models release in the last few years a graphics hardware problem is a hardware problem because the graphics "card" is integrated into teh logic board.