Yep, first, of course, unscrew the little knob all the way. Then, before installing the pump chuck, press the knob in briefly to let out of burst of air and assure that the valve is not stuck closed.
Also, when tightening the little knob tighten it only just barely finger tight -- don't try to get it super-tight. If you overtighten the valve you distort the rubber seal in the valve and shorten its life (in addition to making it more likely to stick).