My iMac 21.5" Mid-2011 (i5 2.7 GHz) has started exhibiting a strange behavior where small colored squares, about 1/8", appear all over the screen. They then proceed to dance around the screen as I continue to work on the computer. I've attached a screen shot. From searching the forums it appears others have this problem, but I am unable to find any threads that actually contain a fix. Any help would be very much appreciated!
That's great news, unfortunately for me the closest apple store is 4 hours away. I'm going to try to try the gpu heat up trick from YouTube. I figure I don't have anything to lose since I was going to buy a new video card from that website I mentioned earlier.
iMac is still running great over a week later. I'm calling this one solved!
I know this is an old thread, but I too was having this same problem on a 2011 iMac. I upgraded to the macOS Sierra beta hoping maybe it was a driver issue only to find that it still did it. I tried all the other solutions, zapping PRAM, turning on reduced transparency, etc. but nothing changed. Meanwhile I was really annoyed by the wiggle to find your cursor feature they added so I disabled that. Lo, and behold, I have not had another issue since. This has been a week ago now and it was an everyday occurrence.
So it's been four months since my video card was replaced and my graphics gremlins are now back. Blaquespell, you said that you disabled a "cursor feature" which seemed to help. Can you please elaborate on what you did?
Go to System Preferences | Accessibility | Display | uncheck "Shake mouse pointer to locate". It's the feature in El Capitan and Sierra where the mouse cursor scales up big when you wiggle the mouse quickly. I would love to say this 100% solved it, but I have had an issue once or twice, but no where near the level it was before.
This problem began for me a few years ago. I took my Mac to a local authorized repair center instead of the Apple Store because a 27" iMac from 2011 weighs a ton and I didn't want to drag it through a shopping mall to the Apple Store. The local repair place has a parking lot and I can just carry it in.
They tested it and said the graphics card tested bad. So I had it replaced. I forgot what it cost but it wasn't cheap. It worked fine after that but the hard drive tested bad so I had that replaced, too. Between the two repairs, I spent close to $750. At that point, I vowed not to spend one more cent on this Mac.
Lo and behold, a few months later, the problem started again. At first, it wasn't too bad but now it's back to the point where it's freezing my iMac. I want to throw this piece of junk out the window and buy a new iMac but I just lost my job and I can't afford it. I don't know what I'm going to do.
So, there's the correct answer. Throw the iMac out the window, being careful to make sure it doesn't land on anyone.
Small squares all over screen
