Download the following utility that will help with troubleshooting your USB problems:http://www.nirsoft.net/utils/usbdeview.zip
Execute the following command before connecting the Arduino to the system:
USBDeview.exe /stext before.txt
Then connect the Arduino to the system and execute this command:
USBDeview.exe /stext after.txt
Send both text files created to this thread. (before.txt and after.txt)
This will give a snapshot of all the USB devices on your system and their states. Hopefully this will point to the problem.
If you run the tool without any command line arguments, it will give you a GUI interface that will allow you to do all kind if things with USB devices. I find it a very useful tool for USB troubleshooting and development.