It's inevitable. At some point, your Mac will need to go in for repair. Maybe the screen cracked, the logic board failed, or water damage...

Try Booting on Safe mode Before restarting your iMac on safe mode make sure you had only connected to necessary items like keyboard and...

Are you here because your iMac screen stuck on the apple logo while booting up? This is one of the most common issues with iMac. whatever...