I just filled up my 10 Gallon LP Gas Cylinder but no gas is coming out of the valve. Even when I have opened it up completely. How can I fix the valve or should I not mess with it?

You filled it up or you had it filled up?

There are safety devices on newer tanks best to take back where they filled it and have them see what the problem is.
DO NOT mess with it yourself.

Nothing should come out of the tank unless you have it connected to an appliance. That is one of the features of the new OPD safety valves. If you open the valve without it attached, nothing should come out. Please be more specific.