1998 Volkswagen Jetta car shut off - won't start

Does the vehicle crank? If so, ensure you have fuel and spark. If you have both then I would test and repair the coolant temperature sensor by either repairing a shorted or broken wire or by replacing the sensor.

Your ECM looks at coolant temperature on start-up as well as a few other sensors. If your temperature sensor is out of range, it could be putting out too much or too little fuel to ignite the combustion process.

Goodluck.