I had this happen on a battery pull due to a freeze twice in a week. I had recently purchased a Bluetooth headset and haven't had any problems since I stopped using it. The only remedy I found was a hard reset. The nice thing about WP is the way it pulls your contacts from windows live, fb, etc makes getting everything back relatively painless. You'll have to re-download your apps but not to worry, the marketplace keeps tracks of your purchases so you won't have to shell out again.