Hey Cyberion,
Could the battery have died? Or perhaps there is a glitch with the battery itself? Usually if the battery loses all of its charge (perhaps do to the lack of use for a while, or forgetting to charge it), all the memory that is stored gets wiped out. This was the case with my Compaq Ipaq. I always made it a habit to hot sync all my stuff to my computer just in case something like this happens...
I too learned the hard way... But it is a good lesson - make sure the unit is charged, and be sure that you hot sync every night!
-SlickVic78