iPad locked up after trying to install iOS 4.2

I am not a developer and tried to install the new iOS 4.2 beta on my iPad. But Apple detected that I wasn't a developer. It didn't allow me to activate my iPad. Now the ipad is stuck on the screen and locked up.When I want to restore the iPad by iTunes and plug-in it, I get the following messages:"We are unable to complete you activation.This device is not registered as part of the iPhone