juju is right.
One day my subwoofer amp started shutting itself off for no damn reason. Out of the blue (I was on the phone with Richie77 at the time).
Turns out that the subwoofer it was running - whoever put the speaker in had pinched the wire between the speaker surround and the wood. The speaker insulation broke through when someone tightened the screws for the speaker earlier that evening... and the amp was simply protecting itself. Cutting off the bad portion of the wire, and properly reconnecting the speaker, solved the problem. Amp hasn't cut out since.
Did I ever tell ya'll about the 3.7 cu ft 12" home theater sub I built? It rocks.
But only when it's not in 'protect mode'