How to fix "out of range" message when phone is on base?

The problem is basically that the phone has an "out of range" message even when sitting on the base. There are two handsets and they both display the same message. There is no dial tone, there is nothing when trying to access the line. I have Vonage phone service and I am sure that the internet and the phone adapter are working. I don't think that it is a power issue either. Any help will be greatly appreciated. Thank you.