How To Fix The Volume Button On A Straight Talk Zte Merit Android

the button on the side of my androide phone was working fine until this morning. Now it is acting up and everytime i push it to turn down the volume or try and put it on silent. it freezes and goes to the blue tracfone wireless inc screen and then goes to the locked screen funsction where i have to unlock my phone and it pauses before everything shows up on the screen. it also occasionally says something about there not being a sime card which is dumb because there clearly is. This sign briefly appears on the locked screen ever so often. What is going on and how do i fix it!!!