My Samsung galaxy J7 recent apps and back button have stopped working. What do I do?

[Yoshi37]

I was walking home from by bus stop while listening to music and decided I wanted to change the song. When I pressed the back button to get to another song nothing happened. I thought my screen was just dirty so I ignored it and tried to use the recent apps button but that didn't work and now I'm here. I don't know what to do.

 

[B. Diddy]

Welcome to Android Central! Have you already tried rebooting the phone? If it still happens, see if it goes away in Safe Mode: https://support.t-mobile.com/docs/DOC-30290