2010 iMac. Half-way through boot it makes a click sound and shuts off. I'm thinking it is the hard drive but it happens repeatedly at roughly the same point in the boot-up. it boots fine into the Safe ...

Safe Mode is a basic diagnostic mode for your operating system that starts the computer without most of its drivers and software. You can use Safe Mode to solve ...

I've tried the verbose boot mode (hold command-v while booting), safe mode (hold shift), and single user mode (command-s). Nothing. It does not get past the grey screen or show the Apple logo.