It looks like something was corrupted and now the N800 needs to be flashed again.
You don't have to many apps installed so that would be a plus!
After flashing the device just add back your apps.

If you have any problem after flashing, we here will try to help.

Read this from your PC you will find many answers in there including "how to update firmware (i.e. flashing new firmware)":

http://tabletschool.blogspot.com/200...ents-page.html