Sherri20,
If there is an entry for a network adapter in Device Manager that has a !, ? or red X on it then it most likely needs the driver reloaded. The drivers for the Inspiron 6400 (available on the
Dell support website) should be loaded in the order below. I've included links to the latest driver for those that I know are correct for your system (usually because they are the same on all 6400s).
If you have any questions on getting the drivers loaded I will be more than happy to answer them.
Larry
Dell Customer Advocate