Check in your settings and you can adjust the toggle switch settings to either mute or rotation lock.
To check first toggle the lock switch on the right hand side next to the volume buttons.
If this produces a bell on the screen this is set to mute.
Now double tap the home button (bottom) and the multi tasking bar will load up, now swipe right and the iPod controls will show, next to that should be a button to the far left with a arrow rotating. Hit that and hopefully this will resolve your rotation issues.