Please try turning the valve in both directions, occasionally the valve will be stuck in the open position. Because the gas can't escape unless engaged with the pin in the regulator, you should still be able to use your tank. If the valve is still stuck, a small bit of oil such as WD40 or cooking spray, applied to the stem should help loosen it up. Do not use any tools since too much torque may result in the valve breaking off. Please let me know what happens.