oh..sorry...
I meant if I turn the player "off" and connect it to USB just the start-screen-picture appears.
Usually it shows the loading progress, but it isn´t shown - just the start-screen picture. :'(
and it just goes so far and not further...
UPDATE: S O L V E D !!!!!!
For everybody who have a nearly analog problem than me,
here a - may be dangerous - but working last alternative:
Open the player - remove harddisk - start again without hdd and connect the player at USB - than connect the hdd with the player (be careful - every pin should docking at the same moment) - and wonder - The PC will detect a new hdd!!
Now you can put the original or rockbox files at the hdd and screw the player together.