Why is no oil in my furnaces' oil filter?i changed filter and now no oil goes to it from tank.how can i fix?

i took vent screw out and still nothingWhy is no oil in my furnaces' oil filter?i changed filter and now no oil goes to it from tank.how can i fix?
Fire up the furnace the pump will pull the oil through. You might have to open the bleeder at the pump. Or just let it cycle a few times.