Hi,
I have struggled all day with my Dell Inspiron N4050 laptop with the same problem. Wasting almost 20 hours and trying every bit of chances I have atlast found the solution of this limited connectivity problem for my laptop. Here it is how:
Going to the Network Adapter device's properties, I have clicked "Update Driver". There I've selected the option to browse my storage for hardware drivers. Locating the folder of all drivers which I got from Dell's website extracted in that folder, Here, Windows showed only the compatible driver in the list, though that was been installed automatically. There is check box denoting something like "show incompatible drivers". I chose that and there I got the name of my adapter's manufacturer Broadcom. The thing is, Windows detected a driver which was actually supposed to be the driver of my adapter which is Broadcom 802.11n Network Adapter driver which in this case been installed automatically by Windows as I saw driver's name and adapter's name to be the same. But from the list of all drivers, I tried Broadcom 802.11 Multimode driver which favoured my luck. I installed that incompatible driver from the incompatible adapter driver's list and found it to be working only after a simple Wifi off/on procedure.
May try incompatible drivers something to check your luck. My one worked fine.
Best wishes!