Welcome ,I will give a full and clear answer to your question, please make sure to reply to any questions I have. They may be essential to my reply.
Please try the 4 digit code , used to unlock the iphone from sleep etc , to unlock the backup when prompted for password to restore etc .
This may fix the problem .
Unplug the USB cable from iPhone.Hold down the center button for about 25 seconds or until the phone turns blank.Plug the USB cable in.Go to iTunes.Right click on your device(iphone nick name) and select Restore from backup.Use 4 DIGITS number key code , NOT iTunes password. Go through all your numbers and one will should work.
Does this help?