How old/new are the speakers? If the speakers are damaged, then it may explain everything. If they were installed 20 years ago, then it would be somewhat unusual for a new issue to suddenly develop with the wires, but not impossible.
I would get a inexpensive multimeter and do some measurements. Ask here, ask how, but I would do a continuity check first with no speakers connected. Ensure that the wires are good. Then measure the speakers.