if yours doesn't seal try pushing the valve to the inside fairly strong whilst you inflate it (with a compressor obviously) this way it will make contact with the tire bead and seal, and what do you mean by "mount" ?
@False: try as i said, push the valve in whilst pumping air in, or at least that is what i would say, my tire didn't want to seal until i did that, go to youtube and this guy "bikemanforU" has a great video explaining it. Check it out.