line is probably plugged with carbon. You'll have to take the line off and replace it if you cant unplug it. Try compressed air if you can but watch out for the mess!
I would suggest that you do away with the drip valve and buy yourself a carburator - it's much safer and you should also install a thermostatic fuel
shut off control valve - shuts down the stove incase it gets too hot.
If your fuel is coming from a day tank - check the vent and make sure it's clear. If the vent is plugged, you're out of business. If the fuel is pumped to the drip valve - make sure the pump is still working.
Carbon build up is the most common problem.