Not to duplicate the web but hit dell.com with your service tag to get the drivers and APPs!!!! Dell uses a QuickSet app to turn on wifi.
I know this is your first time but with some million posts about this issue, I'll keep this short.
I wiped clean an on dell laptop. when I installed win 7 on that hard drive it boots to win 7, but device manager shows many unknown devices. audio does not work or built in wifi is not working either???