Had a similar issue with my 15 watt spider IV, POD X3 Live. Can't tell you exactly what I was doing when it went out, just that it went from working to not working.... It was extremely muted, Likely what psarkissan described. Couldn't get anything to work with the amp and ended up doing a factory reset and that resolve the issue.
How do you soft reset (spider IV 15)? Or is there a specific way to 6 the mute issue other than hard reset?
Since I the problem, I've changed how wine turn the amp on. Master volume gets turned to the lowest position, anything plugging into the amp is at its lowest position then I turn the amp off. Turn the amp on but 1st everything is in its lowest volume position... Haven't had a problem since.