TS1538: iOS: Device not recognized in iTunes for WindowsLearn about iOS: Device not recognized in iTunes for Windows
Currently Being ModeratedFeb 3, 2013 5:41 PM (in response to iris169)
Are you referring to the backup password, or the password to unlock the phone? If it's the backup password keep trying passwords that you might have entered when prompted for a password if you didn't read the prompt carefully - your Apple ID password (or earlier versions of it if you change it periodically), the password to log in to your computer, if it's a corporate computer or has access to a corporate domain, the domain password, etc.
If you can't find the right password you will have to restore your phone as new and reinstall your content.
If it's the passcode to unlock the phone when it's asleep see: http://support.apple.com/kb/HT1212