A) More information is needed to help you trouble shoot this issue. Any time you post on a forum it's always a good idea to list the exact product you are having trouble with.
B) Have you calibrated your touch screen? Many times, the software that comes with the screen includes calibration software. Sometimes it's just a 4 point calibration, sometimes it's 9, sometimes it's 25.
C) Has this screen been molded into the dash of your vehicle or is it still just in the original housing?