You haven't mentioned if you've checked the common things first. There should be an WiFi indicator light on the laptop; if so, be sure it's lit. There is likely a switch or function key which turns the WiFi on/off. The switch is usually located around the edge of the laptop somewhere.
I have a second Dell Inspiron laptop that I planned on giving to my niece for Christmas. It has Windows Vista. I reformatted it so it would be as new for my niece. Before I reinstalled Windows the laptop had internet and wireless connections. Afterwards I am unable to connect to the internet. It cannot find any networks even though I have that available and use with my other laptop and could should be able to connect to it but I can't. I installed all drivers and such from all the disks and it still claims there's no internet connections. What do I do now?