in most cases the batteries in the flash are dead or at least nearly dead. you can change the batteries, there is a nice how-to here http://www.rwhirled.com/landlist/how2-365batt.htm
concerning the pack which jams: it's probably the timer. you can interchange the back doors. if you have a spare pack 100 camera without timer you can switch it quite easily. if you don't have one, you can find spare parts here http://www.landcameras.com/ I have dealt with them and I was pleased with their service.