There are a couple things this could be:
1. Broken coupler in the SC nosedrive assembly.
2. Broken or missing SC belt.
3. Boost Control Solonoid.
4. Boost Control Actuator.
1. Remove the belt. Spin the SC by hand. Is there some resistance? Can you feel the rotors turning? If so, it'* fine, but if it'* a little sloppy, you may have a worn coupler, but that'* not your problem. The coupler would have to be severely broken to cause no boost.
2. Make sure both belts on the engine are in good condition.
3. The boost control solonoid is attached to the front of the boost control actuator. It can be bypassed if you do a search here on 'boost bypass' or 'BCS bypass'.
4. Test the BCA as John suggested. It may help to have a friend in the car. Set the emergency brake, hold the foot brake also, block the front wheels, and rev the engine in gear while you watch the BCA from the side of the car. Don't stand in front of it.
Where are you from, and what language do you speak?