Download the lates Driver from
http://developer.motorola.com/docstools/USB_Drivers/Handset_USB_Driver_64/Handset_USB_Driver_x64_v3.7.0.msi

You have to register as Developer first.

Don't start the MSI, it will not work.

Create an Folder "C:\Driver"

Decompress the MSI-File (Start/Run CMD):

msiexec /a Handset_USB_Driver_x64_v3.7.0.msi /qn TARGETDIR="C:\Driver"

Since we have no "add hardware" in control panel, we have to install this driver manually.