You don't say what sort of guitar you have, or whether this is a new guitar, or one that has worked previously, but it is possible that the pick -up(s) are faulty(if new) or that the wiring from the pick-up(s) has come loose. Also there could be a problem with the pick up selector (if it has one) or the volume cotrol switch on the guitar ~ does it crackle? Do you get any sound at all? It could also be that the wiring to the socket for the guitar has a fault. if you are not a competent electrician, best thing to do is take it into your local music store and ask them to try it out for you.