Mac Display Issue's - Not Green Screen Problem.

My Mac inadvertently Freezes. Breaks up into many uneven, vertical rectangular box like lines trimmed in black. You can still see whatever page / display behind whatever is happening. I have brought it to my local Genius Bar only to be told it was the green screen and that a fix was forthcoming. This was about a month ago. Since then, I have researched the Green Screen and none of the pics I have seen of the green screen match my issue. All advice and information will be greatly appreciate. Thanks, . Thanks