Welcome to the Apple Support Communities. After reading your question, my suggestion would be to check the side switch to see if your iPad Mini is mute. The following article will give some steps to check to see if it set to the option that you want. If you flip it on the side to see if the mute turns on or off or shows the Lock Rotation symbol.
David's suggestion above will work if system sounds are muted. System sounds are keyboard clicks, email notifications, app sounds and those types of sounds. You will still have sound in the Music App even if system sounds are muted. If the tips above don't work and you have no sound at all - even in the Music App, try rebooting your iPad.
Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider if it appears on the screen - let go of the buttons. Let the iPad start up.
This is my explanation for how system sounds (and the rotation lock) can be controlled.
System sounds can be muted and controlled two different ways. The screen lock rotation can be controlled in the same manner as well.
Settings>General>Use Side Switch to: Mute System sounds. If this option is selected, the switch on the side of the iPad above the volume rocker will mute system sounds.
If you choose Lock Screen Rotation, then the switch locks the screen. If the screen is locked, you will see a lock icon in the upper right corner next to the battery indicator gauge.
If you have the side switch set to lock screen rotation then the system sound control is in the task bar. Double tap the home button and in the task bar at the bottom, swipe all the way to the right. The speaker icon is all the way to the left. Tap on it and system sounds will return.
If you have the side switch set to mute system sounds, then the screen lock rotation can be accessed via the task bar in the same manner as described above.
This support article from Apple explains how the side switch works.