You should be able to solve this by, don't get nervous, starting with a new city. I can almost PROMISE you, this should take less than one hour. Start playing the new city, just as you did before. Follow all prompts, including placing buildings, making metal, etc. Soon, you will be asked to sign in to Facebook, Google Play, or maybe the App Store. Once you sign in to whichever one you used to sign in before, using the same information, you used before, you SHOULD BE asked which city you would like to keep, either the one you just started, or your "old city". Select your "old city" and you should be back to normal, happy gameplay. I really hope this helps. I don'the know what I would do if I lost my city. *Fingers crossed* for luck :-)