Help! Imac won't start. I just get gray spinning loading screen.
I unplug to shut it down. I've left it overnight and it still won't start.
Any suggestions?
Brian
Here is the Apple article which is very symptom to your problem.
Step1: The very first step while dealing with a boot failure is to completely secure your data. If you want to preserve the data of your startup drive and don’t any backup, then first try to take a backup before doing anything else.
If you have backup, then skip this step.
Step2: Now, press and hold down your power button until the system shuts off. Disconnect all the wired devices except those necessary to boot. If you can boot now, one of the devices you disconnected, or a combination of them, is causing the problem. Finding out which one is a process of elimination.
Step3: Try to boot in safe mode. If the FileVault is enabled, you can’t do this.
Safe mode is much slower to boot and run than normal and some things won’t work at all, including wireless networking on certain Macs. For more information, refer
this article from Apple help form.