If the wax has separated into two chunks of wax when the wax is cold it will not flow until they have been rejoined. To fix this let the lamp fully heat up. If the wax at the top wont melt hold a hair dryer on the top part of the globe until it does. Gently flip the globe several times until the lava forms lots of small balls. You will have to do this several times but be sure to not shake the lamp up too badly or it could become cloudy or ruin the lamp.