Dave, welcome to Android Forums! Hope your experience here is helpful.
Try these three things:
1. Go to Settings > Mobile Network and make sure that you have a Network operator setup and an Access Point Name set up. Your carrier can give you the correct settings for both.
2. Go to Settings > About > Software updates and see if anything comes up. If so, install it.
3. If you're on the latest update, try a factory reset and see if that solves it.