It might be a stupid question, and please don't be insulted, but I've made a bunch simple mistakes over the years by not having the amp hooked up to the battery or a speaker lead loose.

Just the other day I was set to crack open a Tx case because the servo reverse switch wasn't working. Then I realized I was switching the wrong channel.

If you haven't, I'd test the speaker on it's own, then go down the list of volume, amp, etc.