Renault Scenic 1 1.8 petrol Stop light on ?

Just towed my son home, His alternater belt shredded and some of it wrapped around alternater and obviously put a strain on engine so the safety system cut in and stop light came on. I cleared the tangle and tried to start the car with what little belt there was but it just makes a werering noise. I presume that the system needs resseting can anybody give me any advise as to what is needed to get up and running