Towing Issues: My Tow Truck, key switches, electronic issues

Question
My tow truck was running perfectly fine but now all of a sudden it won't start. Once in a while, it starts for about 6 seconds, but then turns off again. It's a Nissan UD HD1800 2000. PLEASE HELP!!! What is wrong with it?

Answer
well, without being there and checking out a few more things I kind of have a few basic answers...

GOT FUEL ?

They have an electric fuel shut off system also though the fuel pump which also can be part of the problem.  

Plugged fuel filters might be the reason also...

Sorry but its one thing that you have to just work out the very basic things first. Then you can start looking at things like bad key switches, ECM's and other electronic issues.