Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
A power surge can damage some part of an electronic device quite severely.
In this case, I'm not sure what was damaged, but something in the audio amplifier is at fault, if audio signals are not being amplified.
Was it powered through a surge protector?
If not, the damage may be anywhere altogether.
But if sound is not being produced by speakers hooked up to it, when sound input is definitely being input to it, then the best way to tell where that is breaking down, is to measure the signal strength along the signal path, and see where it ceases to amplify... or even, where it ceases altogether. That stage of amplification is where the problem , or the greatest problem at least, is likely to be found.
(An oscilloscope and a schematic and/or troubleshooting tables are ideal for this, but you may not have these, I am aware.)
Let me know if I can advise you further, in any possible direction for solution of this problem.