A lot more information if anyone is to do more than make random guesses. We'd like to help, but we're not psychic.
Without any information or details all I can suggest is a brute force, sledgehammer approach. Download Kies from the Samsung site and install the most recent, full OEM image. That should obliterate whatever software issue that you have. And your personal information too.
If you have dropped your phone and physically damaged the button, then have the button replaced.