I answered same question elsewhere
" I have a very elderly Medion Pocket PC Every so often the same happensas I plug it onto the docking station/charger .
I was told by a Medion engineer (and it sems to work) that if a soft reboot does not work then open the back and switch off. Recharge for 24 hours. Switch on try reboot , prob wont work,. Repeat as above for up to 3 times and eventually it will reboot.
Hope this works for you! "
dekrowrevo, December 2007