I have a two year old iMac which has developed what seems like a major problem. With no warning, rows of small squares appear on the screen and the system freezes. When I try to restart a screen with a brown background appears with the message (in several languages) that I must press the power button until the system shuts down and then press it again to restart. However, when I do that I again get the same screen. I booted up in safe mode with no problem and ran a virus scan with Avast. I cleaned the system and it booted up fine, but then reverted to the screen with the squares and froze again.
Do any of you have any idea what's going on?
Do any of you have any idea what's going on?