Chosen Solution
So, my mid-2011 iMac suddenly became ‘obsolete’ by Apple standards in Jan 2019 and funnily enough a few months later I start having my first issues with the system in 7 years. I’m running on High Sierra and have been for a while, yet upon booting up my system one day was met with a long load screen and a message saying my Mac OS can’t be installed. I reinstalled High Sierra which seemed to work but a few days later was met with the same issue. Even when the system is working my boot up times are noticeably slower. Does anyone know some other possible fixes?
OK, it’s starting to should like you have a failing drive. Lets run Disk Utilities First Aid on the drive, did it pass without error? Can you give us the specs of the drives Make & Models Update (04/20/2019) OK, If the drives passed Disk Utilities First Aid then I think your issue is a mis-match with your OS. You see High Sierra is the highest version your system can support. It appears some how your drive is being upgraded to Mojave so when you boot your system up its reporting the OS (Mojave) is not supported on your system which is technically correct from Apples perspective! Did you click on the Mojave upgrade some how?
