Hi, not sure of your technical level so start with basics..
Is the phone on Vibrate only? Press the volume up or down and it will say at the top.
Is the volume turned up high enough to hear?
Is the speaker working, test it by placing test call on speaker phone or playing some music or changing ringtone to test it.
If all above fail then do a soft reset by holding the power and volume down button for several seconds until it flashs and you see the Nokia logo, don't worry nothing will be deleted and test it again.
Good luck!