The two computers in question are running Fedora 16 & Windows XP. Fedora is desktop, Windows is laptop. Wanted to watch Netflix, can't do it in linux so I hooked up the laptop to the KVM switch, got that working, but no sound. Switched back to the Fedora, where sound was working perfect but now...no sound there either. Re-booted both machines, still no sound. Dis-connected the Windows from KVM, still no sound from Fedora. Re-booted Fedora, still no sound. What happened? I have no idea.

I suspect that the KVM switch itself has no bearing on this unless it is somehow physically defective and taking something ground, but that sounds farfetched even to me.

Have you verified that the speaker jack(s) and wiring did not get dislodged or damaged while you were jockying with the KVM connections? Also check your mixer settings on both machines; I doubt you'll find anything, but it's worth it just to rule them out.

The laptop is not connected via KVM, on its own and no sound. Fedora machine still has no sound. This is by far the strangest thing I have ever encounted in my 27 years of computer use! The KVM switch is still working, or at least the keyboard-video-monitor part, but what other part is there to a KVM switch? I know it sounds very implausible that the KVM switch caused this, but it's the only thing that these two computers have in common. And the fact that the laptop is not connected to the KVM right now and there is still no sound makes it even stranger.

Yes, it is strange.

Here's a thought. Boot to a live CD of something or other and testing the sound. If the sound works in the live CD boot, that narrows the problem to the software load on the computer. If it doesn't, probably hardware.

It would be truly bizarre if both of them suffered hardware failures at the same time, but stranger things have happened.

If you have a meter, you could try metering out the KVM switch to make sure it doesn't have any crossed wires.

Is it a powered KVM (like you will see for a bank of computers) or a non-powered one like the one I have between two computers even as I type? If it's powered, meter out the ground to make sure it's not faulty.