Unfortunately "it doesn't work" isn't much to go on. It could be a hardware problem, in which case a repair is the only thing that will help.
If it's some strange software thing then maybe a factory reset will fix it, unless it's a problem with system software (e.g. you received a system update and it failed after that), in which case a reset might help if there is a conflict between your new software and the existing settings, but won't if the updated system software is itself faulty. If you have rooted the phone and modified the system software in any way then returning to stock is the first thing to try.
Long story short: given the very limited information available, options are factory reset, reflash the device with official firmware (a Samsung PC app called Kies is I believe used for this), or get it repaired. Which will be the answer will depend on why it isn't working, but we'd need more information to even take a guess at that.