I had a similar problem when I installed in-wall speaker wire. It drove me mad until I figured out what I had done. This was twelve-gage wire, but had very fine strands. When I re-inspected my in-wall terminations I found that there were maybe one or two fine strands that were touching. Surprisingly if I ran the system at low volume all was well, but if I turned up the volume it would shutdown. Check you connections carefully, and you may find your problem. Here is an old adage from A&P Mechanic’s School: If you have worked on a system that functioned correctly before you worked on it, and you now have a problem. Go back and inspect what you have done. Chances are very good that something you did, or didn’t do has caused the problem. We all make mistakes. The good mechanic finds, and corrects theirs before they become someone else’s.