Make sure that you haven't disabled stuff in the system configuration utility before you start troubleshooting. Many people use this as a kind startup control panel (which it isn't) and then forget all about it.

First task when troubleshooting is to isolate the problem, first to which device then to hardware or software. You can do this by swapping out equipment and by booting to a 'Live' CD/DVD, it's not really on for most home users but if you are a tech then you will have loads of equipment laying about.

Laptops often have a physical on/off switch for the WLAN card as well and on some that I have seen it is almost invisible, make sure it's not OFF and the software off switch isn't enabled, on this DELL it's 'fn + F2'.

Also make sure you are logged in as an admin user.