Something is shorting out and tripping a safety feature that protects the amplifier from damage.

try a few simple steps to see if the problem is internal or external.

First make sure that none of the speaker terminals have any loose strands of wire that could be grounding out the terminal and that no wires from the red terminals are touching the component or the black terminals / wires.

secondly disconnect all but one speaker test it to see if t causes the amp to go into protect do so for the other speakers until one trips the protect mode. If one of the speakers is tripping the protect mode it could be a damaged / blown component.

just for fun make sure your speakers are 8 ohms this can be found on the manufacturers website or in your manual. Its rare but some speakers are 4 ohm and they can cause amplifier issues such as tripping a protect mode.

You may have to evaluate the "value" of the receiver and determine if its worth repairing. Many shops will charge a "diagnostic" fee which may be $40 to $80 and remember that parts and an hours labor may not make good financial sense especially if you are talking a unit that is 5+ years old.

Hope this helps