Check all cables are secure and if possible try another tape, if you still dont have sound can you ask a friend to check the tape on their video recorder, if it works alright on a different machine then you have a problem with your machine. Video recorders have two pick up heads, one for picture and the other for the sound. Unfortunately if they have packed up it is not cost effective to repair, you will have to buy a new one or ask on your local freecycle site to see if anyone is getting rid of one due to upgrading kit.