I've got a toad immobilsor on my van, it has a small fob attached to my key ring.
If I try to start the van without it, it simply lights up on the dash and remains silent.
If I place the fob near the ignition barrel, it makes a humming noise for about 3 seconds. I can then turn the key and it should start.
The fault:
Now when I turn the key (after hearing the 3second humming noise) it just continues to hum and doesn't even attempt to start

It has done this once before, after I serviced the van. It turned out to be a loose wire near my air filter. I've had a good look around and cannot see any loose wires. I've disconnected, cleaned and reconnected most connections in the engine bay, no luck.
Any ideas? I think I have found the immobilsor and I would like to get rid of it, but would know where to start.