Why does my iPod 4g auto muting the ringer and alerts?

Well I was at the store and I just wanted to turn off all the volume so I went to settings, sounds and turned off everything. Then when I came back home I wanted to turn everything on, and I did. Then I turned my iPod off and the lock sound didn't work, when I FaceTimed it wouldn't let me hear the ring. I went back to settinngs it muted the alerts and ringers I put it back to what i want it to be and the same thing happend again I tried and tried but it just wouldn't work!!