Q: Audio not working, resets don't seem to fix it...

Hello, I know this question has already been asked, but the answers given don't seem to work in my case.

I have a Mid-2010 iMac with an Intel processor and I'm running OSX Mavericks 10.9.2, after the update the sound has been failing to work. On the top right corner  the audio controls appear in gray as shown below:

And when I use the volume keys on the keyboard the volume display appears at full volume but with a circle crossed with a line as shown in the image:

I have tried SMC Reset, PRAM Reset (3 chimes), Repairing disk permissions and Logging-in in safe mode and nothing seems to be working... Please if there's something else I can try it would be helpful. Im growing desperate