As Mcdye stated, the WS-420 would not have been a factory SC option, but could have been installed by the dealer/stereo shop or by the previous owner. If it was done in a very custom manor, you would have a 1" x 7" hole where it was. if it was a basic install using the provided L bracket to secure it to the underside of the helm, then you would have 4 RCA cable sets and a wire power harness left dangling.
If an amp was removed, good or bad, any speakers it was driving would not longer function. Depending on how the remote turn-on circuit was wired, other amps may also not power up with the one amp out of the system.
I might suggest that you seek the assistance of a shop with 12V marine audio experience. You may have a bad amp, but its failure may be a symptom and not the root cause. Something external of the amp may have caused its untimely death.
Michael
Mikes Liquid Audio