Can you get any smoke out the tailpipe? Keep cranking it a good 15 seconds and see if any is coming out while cranking.
No smoke, no fuel: could be a problem with the fuel shutoff solenoid (FSS), the electric wire that goes to the IP - try running a wire straight from 12V+ to the electric plug then try starting. The FSS should click when applying power, no clicky means its stuck shut meaning no fuel flow
Gray smoke: Glow plugs shot or not turning on. You can bypass the glow plug controller with a pair of pliers or a screwdriver between the BIG posts on the relay if you feel ballsy. Count to 7 Mississippi's (~7 seconds)
Blackish gray smoke: She's trying to fire, either you have too few cylidners hot (some bad plugs), a very clogged air filter, and/or not enough cranking RPMs and need to charge the batts up