If you don't have a backup, you are probably outta luck.
You can try a battery pull and see if that works - witht he device on, pull the battery out for about 30-60 seconds, then reinsert and let the device reboot. If at first it doesn't work, try it again but leave it out for a minute or two.
If that doesn't work, you will need to wipe the device using Jl_cmdr (see the FAQ) and then reinstall the OS (should be a link in the Legacy section -
Latest OS: 8700 4.5.0.313/4.5.0.188 (Multilanguage))