How To Fix Mountain Bike Stem Valve?

I have a never ridden mongoose mountain bike and the front stem ( where you put in the air to fill up the tire) is pushed into the tire and i can't put the pump around it. the stem is okay on the back tire but on the front its pushed into the front tire. i tried to pull it out using a pair of pliers but i still can't get it to attach to the pump PLEASE HELP