Quote:

I didn't have any option but to restart manually. iMac was dead. Had to unplug and then re-plug

Shut down, then restart while holding down command + R ... this should boot you off the recovery disk and give you a menu from which you can run disk utility. The repair process will be much more effective since you won't be running off the same partition you're trying to repair ...

However, if you're actually hearing a grinding noise, it's more likely a hardware issue ...