The first thing that comes to my mind is what kind of valve do you have on your tube? If it's a presta valve, it's kind of skinny with a little metal thing sticking out the top, you have to unscrew the top of the metal thingy before you can pump in the air. If it's a schrader valve, it's a little fatter and doesn't have anything sticking out of the end. Your pump might be set up for presta valves and won't seal properly on the schrader valve. Or to confuse you more it could be just the opposite, set up for a schrader valve and won't fit the presta. Most pumps will go either way. Hope this helps, not confuses you. bikerHen