You probably installed the wrong driver. Anytime I have to d/l wireless drivers from Dell...There is always several different drivers to choose from. Sometimes it's a guessing game. Or if you are lucky sometimes you can click on the driver and see exactly what it is used for.
What is the model of the laptop. And can you use SIW or another sys info tool to identify the wireless card? Did the computer have Win 7 on it prior, or did the customer also upgrade at the same time?