Does the clutch on a 93 sentra have a sensor to start it?

Yes, there is a switch on the pedal, just like on the brake pedal of automatics. There are 2 locks, yours is electric, but the key lock is manual, it has to be on. Which it would be if you were trying to start it, but on the automatic, it goes from the key to the shifter with a mechanical lock, also the brake pedal is wired into a solenoid on the shifter, won't move without your foot on the pedal. Sometimes it has to be in neutral to start. Check it out.