It must be a virus...
This is **exactly** what happened to me yesterday evening on my 680. And I hadn't used the Jornada at all since Sunday morning.
When I arrived home I wanted to test the calibration trick we discussed about yesterday. I opened the Jornada... no sign of life.
Ok, maybe the battery was discarged. I put it on its cradle, connected the unit to the mains... nothing again. I have tried to charge it for hours, but it doesn't give any sign of life. I think I'll open it tomorrow
(if I have time
). I can share some info, if you wish.
Good luck!