Why is there no sound coming from my speaker?

Why is there no sound coming from my speaker?
I'm ready to jam out and I've got my tunes playing, but nothing is coming out my speaker. What do I do?

ANSWERS:

Ear phone jack contacts need to be cleaned. If sound is ok using earphones but no sound when ear phone jack removed, this is the problem. Happened to me 3 times over 3 year period.