Hi katearnaez2930. Welcome to Android Forums. I've never used Viber so I'm not really the guy to come to your aid. I might suggest removing the app and dnld and install it again. Perhaps a fresh install will work for you. I hope this will help.
Thanks for joining our community.
I have never got viber to work on my HTC Desire C. I can text on it but if I try to make a call to another viber user who I know is waiting for the call, I just get a series of beeps. Sometimes they can ring me and I hear them for a few second but it is gone before I can answer. I have tried wifi near the router with strong signal and I tried on 3G network with the same result.
My recipient regularly uses viber to talk to others, so I presume no problem that end.
I've uninstalled and re-installed viber it is the same. Skype works fine on the phone, unfortunately the person I wish to talk most to has reasons not to use Skype.