On rare occasion the 6-pin Molex speaker header pins (inside the amplifier) slip above the path of the 6-pin Molex plug holes. This results in the pins inside of the amplifier not sliding into the plug, and not making contact with the speaker wires resulting in no sound.
If you have no sound and have looked at everything else, we recommend pulling the 6-pin speaker wire plug to see if the pins are bent above the connector path. If they are, it explains why you have no sound because the speaker lines are not electrically connected.
The solution is not complicated; you may be able to plug the connector in at a slight upward an angle in order for the pins to mate with the plug.
If necessary, you can also use needle nose pliers to reach in and bend the pins down a few millimeters each and attempt to re-plug the connector after the header pins are better aligned.
This is an extrepely rare failure mode since all of our amplifiers are thoroughly inspected and tested but it is possible to have a failure in the field.