On Wednesday, October 28, 2015 at 2:26:55 PM UTC-4, wrote:
I have a pair of Powered Computer Speakers JBL brand. They worked fine,
and suddenly there is no sound. I did not blow them by too high volume,
in fact they were shut off, and when I turned them on, they did not
work. (I normally have them shut off, since I dont like a "noisy
computer". I only turn them on to play MP3 songs, or to watch a video.

They are powered from a wall transformer, which apparently is working
because when I push the "ON" button, the light lights up, and I hear a
slight click in the speakers.

But they dont play the sound coming from the computer. (Yes, they are in
the correct plug on the computer). Thinking there was a problem with the
computer audio, I plugged these speakers into another computer (which I
know has working audio). Still no sound. I also know that normally,
touching the tip of the cord (speaker input wire that goes to the
computer), that a hum is heard. Now, there is no hum.

I'm assuming that there is an amplifier board inside the speakers, and
it must have somehow died. I have not yet attempted to open them. It
looks like there is a screw on the bottom, hidden behind the stand.
Whether that will open it, is questionable.

I suppose I should just buy new speakers, but these were good sounding
and quite expensive, so I'd like to see if they can be fixed. Have any
of you ever repaired these things? Is there an actual amplifier board,
or is it just a chip? I have my doubts about finding any replacement
parts, unless it's just a capacitor or power supply diode. Or, might
there be a fuse???

Thanks

Before I looked any further, I'd try one more test. Plug a pair of
headphones into the jack where you normally plug the speakers and ensure
that you have sound at the jack.

I know you mentioned "another computer which you know has working audio"
but I'd stick with the system you are using and be 100% sure it's not the
system itself. A different computer adds a another variable. There's no
need for that - yet. First eliminate the original system as the root cause.

Do you have an audio extension cord between the computer and the speakers?
I do and I once found that it had gotten disconnected behind the desk. I
discovered this *after* I determined that the computer was fine by using
a pair of headphones.