You may need to change your Ring Volume. Here are some instructions on how to do so.

To Change your Ring Type:
1. Press the Feature button, then * 6
2. Press the number keys 1 – 4 to hear the different ring types
3. Press the OK softkey when you hear your desired ring
To Change the Ring Volume:
1. Press the Feature button, then * 80
2. Press the volume key up or down
3. Press the release key1 to exit and save the volume level

Let me know if this works for you.