have you tried just hot wiring the starter?
take a wire from the positive battery terminal to the wire that comes off of the starter. That will tell you if the motor will turn over.
from there, put the key in the run position and see if you can get it to start that way.
If it does start, then chances are, your ignition switch is bad. Happens in older nissans. Pretty popular with 240s...

Also try that ^ jumper trick too. That switch is what won't let the car start if the clutch isn't all the way down. If that switch isn't working, then the car doesn't think the clutch is ever down and won't start...