Chosen Solution
Alright so, as you can see in the photo that is how it looks like. My Mac is from Mid 2010 21.5” with 4 GB RAM, running on High Sierra. I have tried searching for a solution online, but I can’t find anyone, who had the same problem as mine. What I’ve tried so far: Reboot and redownload everything. (Deleted the whole Mac), and still the flickering is happening and keeps shows up.I’ve tried reset NVRAM and SMC, still did not work.Start up on recovery Mode, still did not work. (Also I pressed down D).Updated newest software. Symptoms other then the flickering screen: I woke up this morning, and the flickering was gone for like 20 mins, and came back.The computer is heating up a lot.The computer ONLY STARTS UP if I hold the down shift key! If i start up normally, then it freezes halfway through booting/loading. (or opening or whatever you call it) This confuses me, and I hope someone can help.
Ah! Confusion! Lets step back for a sec … Your system has two graphics services! One within the Intel CPU its self (Intel HD Graphics) and a second discreet GPU MXM board: ATI (AMD) Radeon HD 4670 or Radeon HD 5670. So what happening here is you are jumping between them! When you startup pressing the Shift (⇧) key you are using the Intel HD graphics as the AMD GPU board drivers are not loaded. Reference: Mac startup key combinations Where does that leave us? You have a failed GPU board which will need to be replaced, this is not a software issue! iMac Intel 21.5" EMC 2389 GPU Card Replacement
