Welcome to the forum.
My speculation based on the symptoms is that there is one or more amplifiers connected to those speakers that has an enable / disable amplifier input signal and that input is not at the enable level.
It will likely take some sleuth effort to track things down, starting at where things are working.
The tools I find handy for this type of project are a set of unpowered speakers, a set of powered speakers, such as would be used in an old desktop computer and an audio source, such as a hand held CD player w/ an RCA audio output. These tools are very handy to have known good parts for connecting to unknown parts.
