You can try a hard reset of the device: pull the battery from the device while still powered on. Leave it out for 30 seconds, then reinsert. If you have installed applications on it recently it might take a little while to reboot.
If it's been like that for a while it's likely you'll have to reload the OS to the device. If you don't have a backup (it's not possible now) or are not on a BES (usually on corporate BB's) then your data is gone.