Problem with libusb and/or pyusb

I don’t usually post trying to solve my problems myself, but getting desperate now.

My system is a 3.2GHz AMD running 64bit Win-7 using ZEM3010.

I was hoping to get a better control over USB using Tkinter and Python and installed PyUsb and libusb. Now I cannot even GetDeviceCount().
Have any body had a similar problem? What is the easiest way to fix this problem or at least revers it to original configuration?