Have you done a hard reset/reboot lately? Pess both home and sleep buttons until you see the Apple logo.
Whenever my idevices start acting weird, that's the first thing I try.
Edit: do you happen to have Photoalbums+ ? Just saw a post from another user that is also having the black screen with iMessage / SMS messages. http://forums.everythingicafe.com/threads/photoalbums.87274/#post-936952
Thanks roof. I did that. However the culprit was Photalbums+. They had an update and since update not worked so I deleted Photalbums+ for now and it works normal! Thanks. Maybe this will help someone else