Sarah, this can be caused by multiple reasons -
Battery has expired.....ie swollen ,thus preventing menu button function.( batt. Is under top of click-ring)
Bad / damaged click ring ...did a bod stand on it?
If it does not move at all , and is in its original level position,ie not crushed!! Might need a new click ring.....find a geek nearby to do it ,its on utube mostly.....not too diff.