I had this same problem when I first setup my MiFi on my laptop with the Vista OS installed. If you haven't already, try this: go to your Network and Sharing Center/Manage Wireless Networks/Highlight (don't click on) your MiFi connection/Right click/Properties/Security and enter your Network Security key information, which if you have reset the device should be the password located on the back of your MiFi. Try these steps with/without the device being plugged in.
