iMac 21.5 inch display issue (mid 2010)

[fredsarran]

Hi,

I have the display looking all scrambled during the transition between the boot up screen and login screen (only for 3 seconds or so) :

However, the display is fine once logged in. What is the problem ? I phoned Apple and they have no clue.

This screen problem randomly happens, it does not happen every time.

Thanks for any help,

 

[fredsarran]

Solution !!

Ok, so Apple replaced the Graphic card and issue still happening. After a lot of brain storming, I deleted one by one apps/software that starts at the same time the issue is happening, and I discovered it is the Air Display app by Avatron that creates the problem.