iMac shows prohibitory symbol I recently booted up my iMac, but then the Apple logo disappeared and a replaced it. I tried going into Recovery mode but recovery mode just takes LITERALLY hours. No matter how long I let it load, recovery mode doesn't help: I let it load overnight and it still didn't work.

How can I fix this issue and boot into my iMac again?
This happen to me too after I started and then canceled the installation of Mojave.

I fixed it easily by following these steps.


Boot in recovery by Powering up and immediately holding CMD+R
Clicked on Apple logo and choose Startup Disk
Select the Mac OS disk and click restart.


If these steps didn't work then you can try reset. 
WARNING this will delete all your Files


Select Disk util from the recovery menu
Erase Disk
Go back and Reinstall OS