I have a full propane tank that I cant get any propane out of. I know that there is a internal valve that activates if you blow a hose will shut the flow off. How do you reset that valve?

Did you try turning the valve "OFF" and waiting about a 1/2 hour?

I found this, maybe it will help:
Propane tanks are commonly used for heating homes and businesses and for agricultural use. These tanks are available in a variety of sizes to accommodate different purposes and uses. The gas flow on propane tanks needs to be monitored and that is why the tanks are equipped with a check valve. Low gas flow or propane leaks could be an indication that the check valve needs to be reset. Check valves can be reset without calling a professional.

The first step in resetting the propane check valve is to turn the valve the shuts off the container. Twist the connection to unscrew it, which will detach the propane tank from the hook up site.
Flip the valves to the highest setting possible if you are using a gas grill, which will get rid of residual pressure or gas that may remain in the lines.
Turn off the grill. If you do not while resetting the valve, it could be dangerous.
Twist the connection in the opposite direction you did to remove it to reconnect the container.
Turn the tank valve switch to the "on" position. Move the lever very slowly, so the gas goes back into the lines and grill slowly. This will help put the tank back in check.

Tips and Warnings
Propane gas leaks can be dangerous and serious because they can possibly lead to explosions. If you do notice propane leaks, you need to evaluate the problem as quickly as possible before problems develop.

My tank now flows.

Besure to open slow for the reset.

I found this, maybe it will help:
Propane tanks are commonly used for heating homes and businesses and for agricultural use. These tanks are available in a variety of sizes to accommodate different purposes and uses. The gas flow on propane tanks needs to be monitored and that is why the tanks are equipped with a check valve. Low gas flow or propane leaks could be an indication that the check valve needs to be reset. Check valves can be reset without calling a professional.

The first step in resetting the propane check valve is to turn the valve the shuts off the container. Twist the connection to unscrew it, which will detach the propane tank from the hook up site.
Flip the valves to the highest setting possible if you are using a gas grill, which will get rid of residual pressure or gas that may remain in the lines.
Turn off the grill. If you do not while resetting the valve, it could be dangerous.
Twist the connection in the opposite direction you did to remove it to reconnect the container.
Turn the tank valve switch to the "on" position. Move the lever very slowly, so the gas goes back into the lines and grill slowly. This will help put the tank back in check.

Tips and Warnings
Propane gas leaks can be dangerous and serious because they can possibly lead to explosions. If you do notice propane leaks, you need to evaluate the problem as quickly as possible before problems develop.

My tank now flows.

Besure to open slow for the reset.

Do you have access to professional help? Please don't blow yourself up!