Open up the Device Manager (Right Click on "My Computer", select properties - if using 2000/XP, select HARDWARE TAB and press DEVICE MANAGER).
Find your device in the list. It may have a yellow ? next to it, it may not show up as the correct type item.
Go to the properties for that device when located, and select REINSTALL DRIVER. Select the path where your drivers exsist.
That should do it. If not, come back here!