is it jailbroken or unlocked? is wifi turned off?
if it's a stock device and you havent done this already, turn off wifi, and ensure Location Services is turned on for all apps in settings. then go outside with exposure to open sky and a few yards from any tall buildings, open up the maps app and press the bullseye icon in the lower left, and wait. if it doesnt start drilling down to your actual location after a few minutes, try doing a restore in iTunes.