have you ran the mistking with the tube going into a bucket or something after the reservoir went empty? the pump probably has air in it and need to run it into just something like a bucket even can be back into the reservoir but not the nozzle. i have had this happen before and it just needed to be cleared of air as it won't do that itself if its running to a nozzle.
I agree, you have to prime your pump, disconnect the hose on the opposite side of the hose that goes into your reservoir, angle your pump so the open end is up and facing a bowl or something to catch the water when it bleeds out the air, turn the pump on and let the pump push all the air out, once you have a steady stream, re-connect your tubing