Hello and welcome to Android Forums. Hopefully I can help you with your problem.
There's a very good chance that your device ringtone setting is on silent.
Try going into your phone settings. Look for Sounds or something of that nature. Locate the section that says something like Ringtone or Phone Ringtone or something like that. It's in there, you just have to find it. Device settings are labeled differently, you just have to locate where yours is. Once you have, look in there and choose a ringtone. I have a feeling that yours is set on silent. It's happened to me on several occasions.
Also, make sure that your volume is turned up. You can do this on most phones by holding down the volume rocker on the side of the phone. Hold it down in the up position. A display should pop up and let you know what your volume level is. You can also silence your phone and set it on vibrate mode by doing just the opposite. Hold the volume rocker down until it shows that it's silent or it vibrates. If it vibrates then it's in silent/vibrate mode.
You can also adjust your phones notification, alarm, and ringtone settings. Go into your device settings and look for Volumes. Make sure they are all turned ALL THE WAY UP.
If none of these steps help, you've got a more serious issue. Please make another post if none of this works for you.
Best regards,
Wetbiker7
If you have any other questions regarding your device, I invite you to join Android Forums. We have many sections for specific devices which contain a wealth of information.