As of today my mac has no more audio?

Hi,

Today when I turned on my mac I realized I get no sound. What's intresting is I get the dong when I turn it on and I even get the clicks when I drop a file into a folder. What's odd though is I get no aduio when I play on song on iTunes or even when I watch any type of move on the web. When I try to turn the volume up or down, the icons move but there's no clicking sound associated with it. Furthermore when I tried pluging in head phones to see if my speakers had gone bad, there was no sound there either. So my question is what do I do? I treid resetting the PRAM and some how (and I really don't know how) erased my harddrive. I thankfully had a back up and all is good now, except no sound. I did upgrade to Lion a month or so ago, could this be a glitch of some kind?