I have a three year old mac mini, I am running OS X 10.5.8. I was having some minor issues with the sound which seemed to clear up. Now I have no sound externally or through the phone jack. Itunes will not play. The volume screen shows full but there is a circle with a line thru at the bottom. I changed the hard drive about 4 months ago and had no problem. I checked all inside connections the other day and all seem fine. Can anyone help? Software/Hardware issue???