Welcome to the forum!
The comment about your friend poking around the speaker wires caught my attention. I know that you said you disconnected them, but it makes me wonder if there's a short circuit somewhere that is causing the Pioneer to go into protection mode and shut down. Try disconnecting all of your speakers, making sure that there aren't any copper wire strands bridging between two terminals on the Pioneer. After that, let us know if it still shuts down right after you turn it on.