Again an additional point :
I had used the USB link in "storage" mode, and it had perfectly worked, but I've had a connector pb, I've stopped to use the USB connection from then, and I've changed my PC configuration several time since.
Now, my connector problem is (should be ?) corrected, but I don't remember if I had made something specific on my Win XP in the first time to have a classical "storage" behavior.
What you say make me fear a hardware problem still existing ...