"protect" mode is there to prevent the speakers from damage. Basically the output lines are monitored to insure that there is no DC voltage present. DC voltage to a speaker results in heat which will damage the voice coil and thus the speaker. This is why there is usually a slight delay from the time the unit is turned on to the time you hear sound. In this case, I would suspect that the output transistors/amp pac have failed. Whether or not both channels have a problem, the unit will go into protect mode.
If you follow the flow chart provided previously, I expect you to end up at the "replace AMP board" section.
It is possible to repair the amp module, but that will take some investigation and perhaps specialized equipment.
Hope this helps,