I have an mp3 player connected to our on hold line. So we are using it in a loop player mode. I have a charger connect to the mains and it has USB port on the front connect to the stick mp3 player. It chargers the mp3 player . But when its plugged in it turns off. Just like when you plug it into a PC. How do I get it to stay on when its plugged in??

If I have exlained it wrong please let me know.