It seems that every new gadget needs to get a reset from time to time. I managed to lock myself out of my MDA but there is a way to hard reset it even if you don’t have the password to launch the normal procedure.
 To do the reset press the Comm-Manager key as well as the Voice Key and do a reset in the little reset whole (use the stylus). Hold the keys even after you initiated the reset. If the black boot screen pops up press the green phone button.
 

That should do it 🙂
 Further information is here and here.