Most likely you have tripped the safety surge valve on the regulator. Here's the remedy. Open one of the burner control valves and relieve the pressure in the piping and supply hose. Close all burner control valves, then just barely crack open the tank valve. Allow the gas lines to pressurize slowly over a minute or so then open the tank valve fully. You should then be able to light and operate the burners normally. The surge valve is designed to shut off the gas flow in the event that a supply hose gets burned or severed. The sudden rush of gas trips a valve mechanism built into the tank connector. It won't usually shut off the gas entirely, but it slows it to a trickle which is pretty much what you have described. Even with the burner valves all closed, there will be a rush of gas to charge the 1/2" black pipe manifold until the pressure builds up and slows the flow.