iMac won’t boot - tried it all!

[Sect]

Hi, I need help! Please!
My iMac won’t boot. It is stuck on the loading screen with the progress bar at 100 but won’t go any further and have left if like that for days.
I have check the drives with disc utility.
I have reset the PRAM/NVRAM and selected the boot drive again.
What I can’t do is boot into safe mode. I tried holding down shift when I boot till I see the apple logo, I have tried holding down the shift for the duration of the progress bar (8 hours still hasn’t loaded - used a book to hold the shift down )

Does anyone have any ideas at all as to what I could try next?

 

[mreg376]

Well, you can try telling us the year, model and configuration of your iMac.

 

[Sect]

Well, you can try telling us the year, model and configuration of your iMac.

Oh right, sorry
It is an iMac core i5 2.7 27-inch (mid 2011)

 

[BugeyeSTI]

Sounds like a hard drive failure. Disc utility doesn’t always show a bad drive. Have you tried to boot from an external drive?

 

[Fishrrman]

Didn't 2011 iMacs have problems with the graphics?

As Bugeye suggested, try booting from an external drive that is BOOTABLE TO THE FINDER.
An "installer drive" won't do.
That can quickly clarify whether it's the internal drive or not.

 

[old-wiz]

A bootable external drive is essential for diagnosing internal boot drive failures. I keep multiple bootable external HDDS from SupeDuper and if the external boot works fine then the internal HDD is most likely dead. I would replace the drive, not try to revive it.