If the player is working OK on the AC adapter, then I would start looking for wiring issues behind the sled.

Your description of how there was a pop from inside the dash indicates to me that there was a loose, frayed, or unexpectedly grounded or crossed wire back there somewhere, and the bump caused some kind of a connection to be lost or made.

I would in particular look at the wiring that runs to the amplifier, including the amplifier remote turn on wire. Perhaps that got grounded or perhaps it is pulled out and is touching a power wire.

You're definitely going to have to pull the thing out of the dash and examine all wires to it and to the amp carefully. Also, if you have any long wire runs from your dash to your trunk, consider the possibility that something is frayed or grounded along the length of that run.