Default [Q] USB File Transfer Problems

Helo all,

since two days I now own an Thinkpad Tablet and am happy so far. Only when ein plug it into my PC (Win7 64bit) via USB it is recognized but I still can't transfer files. When I open MyComputer in the Explorer on the PC I ca see the Tablet, click on it but then no files on the tablet show and I also cant transfer any. It then gives me an error: Device was disconnected or istn working properly.

Tried installin ADB Drivers form Lenovo, switching USB debugging off and on, no help.

When I plug it in on the tablet im prompted with the selection of just charging or MTP. If I choose MTP it makes the same Windows sound as if unplugged....

Any Ideas?