Have you tried resetting your device? What about performing a firmware update? If problem still persists, open up the casing and check the ribbon cables. Make sure they are tight and snug (make sure your device is powered off while performing this step; will void your warranty). If the problem continues to occur, most likely your touch screen digitizer is faulty. It is relatively easy and inexpensive to replace (replacement panels start at around $8 on eBay or any other retailer). When buying a new panel, ensure that model and version number matches yours. Hopefully this helps.