Well, connecting to the track shouldn't kill them unless something else providing power is connected to the track! Shorting the track leads shouldn't kill them or they'd die at the first derailment.
That being the case, my approach is to simplify what you're testing and find out what works and doesn't work. If power isn't coming through the explorer box, it's clearly something internal to the box. If the internal fuse isn't blown, it's hard to imagine what is going on.
