Threshold S/300 power amp problems

Does anyone have an idea what the problem might be where the power amp does not continue to provide sound? While I was working in my office and listening to Bill Evans Trio there was a sudden pop sound (not loud because I was listening at a rather low volume) and then there was no sound. There was/is a slight static sound emanating from the speakers but nothing else. The main pilot light on the Threshold remains on but does not produce sound. I have:

1. attempted to play the CD player.
2. attempted to play the reel to reel tape recorder.
3. checked all cables and connections.
4. made certain the pre-amp volume was turned up.
5. checked all fuses on the power amp. All looked good.

I was not able to get any music out of the system. I will swap in my Audio Research power amp this weekend and see what happens. Thanks for your comments.