When you say hooked up, did you attach the hose to the water inlet that looks like this:
Or did you put water into the tank through an inlet like this:
If you put water into the tank via this connection, your water pump will need to be on to get water.
Also, there may be two of those first connections, if your trailer was equipped with a black tank flush kit. The black tank flush should be marked.
There really aren't any stock valves in the system that would block the water flow.
Here is a generic RV water system schematic that might help you understand that part of your RV:
Sunline Coach Owner's Club - Sunline Owner's Files - Generic Travel Trailer Water System Schematic
Let us know how your hooked up and we can give you some more places to look from there.
2004 Dodge Ram 2500 Club Cab 4x4 CTD
2007 Sunline Solaris T-276-SR: Misty Blue/Cherry
2001 Dodge Ram 1500 Reg Cab 4x4 OFF-ROAD