I disable the onboard wifi and use some other card. Read this one -> http://forums.cnet.com/5208-7589_102-0.html?messageID=3235370&tag=forums06;posts#3235370
Could be that old internal wifi card issue. What slams many owners is they didn't know these do fail over time.
Somehow something changed in my Latitude E6400 (OS Windows XP - Professional 2002, SP 3) and now it has been impossible to connect to any wire/wireless network (Home, hotels, airports, none). Here at home, I have some 5 computers (family) and they all connect to my Wireless network with no problem whatsoever, except this Dell. I try everything I know (not much by the way), and the Latitude gets connected (gets a valid IP address from the router) for 6 to 8 seconds and suddenly it gets cut up and I get the Limited or No Connectivity pop up window and that happends with both wired and wireless. Du you have any idea why this is happening? The first time I brought this laptop home, it worked nicely, and so did at the hotel and office in Houston. The driver for the WL is Interl (WF) Link 5100 AGN.