One of my users Mid 2011 iMac (27") has been not working for about a week now... I'm suspecting a failing HDD but am not sure. Symptoms: 1. Will not boot, shows gray screen with circle and slash through it. I booted to recovery, Disk Util, verify HDD. Says needs to be repaired. Repair fails and it says to reformat HDD. Reformat and restore from most recent TM backup last night. Come in today and it is now just stuck in boot sequence, not even displaying circle with slash. For some reason this time I couldn't boot to recovery using command+R (just kept trying to booth for about 15 min, fingers got tired) but was able to choose recovery partition by booting and holding OPTION. Once again same with disk utility. Reformat and am now restoring from a backup from 2 weeks ago in case it is SW related. Any other ideas? Unfortunately AppleCare expired in June. Is it possibly not the HDD? If it was bad I would not expect to even be able to reformat it and reinstall but maybe it is just 'gradually' dying? Not even sure where I would start if it was the HDD - I can't take this beast apart! Any advice or tips is appreciated!