Since I updated my iPad to iOS 8.0.2 the App Store on my iPad is not working and neither do iMessages and and FaceTime. How can I fix this?
My initial thought would be that your Apple ID is not signed in anymore. This can happen e.g. when you perform an update/restore via iTunes and didn't select to encrypt the backups. Unencrypted backups do not contain login information.
Head into "Settings > iTunes & App Store" and make sure you are signed in with your Apple ID.
Go into "Settings > FaceTime" as well as "Settings > Messages" and again, make sure they are activated and signed in with your Apple ID.
If all seems to be in order I would create another backup of the device and then restore the iPad.
iOS: Troubleshooting FaceTime and iMessage activation
I'll tell you on my deathbed when I finially fiure it out!