AV42 monitor speaker will not power up

My AV42 monitor speakers started intermittently powering off during use, then they stopped powering up at all. I tested the power cable and fuse, and they are fine. I took the back off to look for obvious loose cables but couldn’t find any. I finally found an alternate cable to test it with, so I put the back on with just four screws, and it worked. Tried back with the original cable and it worked. Put the remaining screws back in and nothing. Any thoughts?