Fuses blown and PC backup power ... and a mystéry
It sounds like you have a common mode voltage problem between your audio source and your speakers.

Start looking for a fault from the audio source that is feeding the speakers. Measure the voltage from the audio out connectors (each pin) to the ground on your outlet strips. You should not find anything over a volt or two.

Also measure the voltage from one ground pin to another on the outlet strips. You should see close to zero volts. Do the same with the two round pins between the power strips to make certain that one strip isn't cross wired.