as chrisjr says, check the speaker wiring. That's the most common cause for protection mode. The amp is protecting itself because of a short in the wiring and it's stopping you from using it before the problem is fixed.
If the amp is still stuck in protection mode after all the speakers are disconnected then you might have to do a full microprocessor reset. Be aware though, this wipes all the settings and puts everything back to factory default. Also, it's not a fix. If the wiring is still bad then doing a reset like this won't repair that; all it's doing is letting you start over.
1 Turn off the power using the Standby/Power Key.
2 Press the Standby/Power Key while simultaneously pressing INFO and BACK.
3 Once the display starts flashing at intervals of about 1 second, release the two buttons.
If in step 3 the display does not flash at intervals of about 1 second, start over from step 1.