I have the same problem and I've found the phone has to be HARD reset, I may take mine to geek squad, where they can do the reset and download the info needed for the phone to work. ALL data will be gone including data that came with the phone. You may be able to find and downland on your computer data needed for your phone to operate after the hard reset. I'm not an electronics person and really don't have the time to all of this myself much less find the operational hard data for this particular phone. I may just get a new phone and save the headache!!!
Factory reset doesn't work especially without wifi... Where you hold the power button and volume up button down at the same time......you can try that and if it does nothing the above applies . Good Luck,