Now i can open my ipad. What should i do?
Try a reset:
Hold the Sleep and Home button down for about 10 second until you see the Apple logo.
You should check your iCloud back-up settings after following Divonex's post.
3. Storage & back-up
4. Icloud back-up = ON
Typcially iCloud will back up your device one a day and krrp the 3 latest back-ups for you if you need to restore your device or if you get a new iPAD
Retrieving data ...