Have you gone into "Settings" and then "Sound" and made sure nothing is turned way down or muted? If the problem isn't there, try starting the tablet in "Safe Mode" and see if the sounds work in there. If they do, then it is likely something on the tablet is causing the issue. Bad app, virus, malware, etc. If, however, it still wont give you sounds, even in "Safe Mode", then I suggest having it looked at. Either by the manufacturer (if under warranty) or a local tech if not.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.