I just filled the fresh water tank for our first time on new-to-us 2010 Keystone Alpine. I stood inside, kept testing the water level, it never moved - and then it started to overflow at the outside. ...
If water overflowed at the outside fill port, then there is probably water in the tank but the monitor panel is not working properly. Did you hear the pump running? If not, then there is another problem with the pump, fuse or wiring. If you did hear the pump running, but no water, then it takes some time for the pump to prime, especially if it hasn't run in a long time, the seals may be dry.