iOS 8.3.1 update
UUnable to install iOS 8.3.1 because it asks for pass code. I do not know what this number is
iPad 2, iOS 7
UUnable to install iOS 8.3.1 because it asks for pass code. I do not know what this number is
iPad 2, iOS 7
Try the passcode that (if you have one) you use to unlock the iPad.
If that doesn't work then do you have Settings > General > Restrictions enabled ? If you do then try that passcode
iOS 8.3.1 update