Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Plug it into iTunes and click the Restore button. Do NOT restore it from a backup made when it was on a 4.2 beta.
 
the beta expires? after how long? i'm still on 4.2 beta 1

i don't connect to itunes because that garbage always tries to automatically delete everything of my ipad and iphone
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.