I have no sound -had a blue screen I-tunes came on

I have an IMac OS (10.6.8) I had a blue screen problem & Itunes came on sound was irritating -under stress so I muted the sound. Corrected blue screen & no sound icon in top of screen. Went into sound & scale was at max, & mute on. But is was grayed out & I could not undue mute.Also if I play tune it does not move on bar.HELP!!!