windows iphone not show in itunes 3G

Hi all,
I used to sync my iphone with itunes on my notebook.
I realy dont know what changed but: from one day to the other, itunes does not recognize the iphone any more.
( the cable seems to be ok, since when I connect the iphone to a different computer, itunes fires up ok)
I checked the support page (http://support.apple.com/kb/TS1495 ), so:
i have the usbaapl.sys file in system32/drivers; ok
the apple serverices are running; ok
BUT: the iphone is not listed under USB devices in the device manager
(btw: the windows camera diaglog fires up as expected, when the iphone is connected )
I restarted my notebook, reinstalled itunes, turned the Iphone off and on - no change.
I realy need my iphone to sync again - so please help.
Core 2 Duo Windows XP Pro