Oh!
So with the lens off the camera and looking straight into the mirrorbox what do you see?
You should see one of three things:
1. a mirror with very fine lines running across it
2. no mirror, but a blackened back panel
3. no mirror, no black panel, just a greenish looking shiny surface, which is the sensor itself.
If you can see the mirror, maybe it can eventually come good. Is the battery charged. All I supose you can do is keep trying.
If the mirror is stuck in the up posi, and you see the blackened panel at the back of the cameras inside it could be stuck in semi liveview mode or something.
If the greenish shiny sensor is exposed, you may have a problem, or you could be in liveview mode and it's stuck.
I once had this problem with my D70s and all it took to fix was a dismount and remount of the lens that was on the body at the time.
Are you in manual mode, Aperture priority, etc...???
at least keep the camera in manual mode. If it's in manual mode, even if there is no lens the 'err' code is most likely to disappear, as the any of the auto.semi auto modes will show 'err' if there's an issue with the camera/lens electronic connection.
is the camera responsive to any button pushing at all?
Are there images on the card? if so, upload them to the PC and reformat the card on the PC.
hope it all works out for 'ya.