1. Is your computer detecting your wireless card ok, go to Device Manager to see if there are any yellow ! or ? by the network device "right click my computer" >> Manage >> Device Manager
2. If you see yellow ! or ? you need to reinstall the driver most likely if not go to 3
3. Does your computer have a switch to toggle on/off wireless. It will either be a switch allow the sides or front, a button above the keyboard or you have to hold the "FUNCTION" key might say FN and hit the wireless icon usually located on one of the number or F keys.
4. If thats off turn it on and rescan for networks it should work now if not go to 5.
5. Turn of your computer and turn it over and look for your wireless card, you will neede to remove a panel on the back. It is usually located by itself or in the same area as memory. Memory panels usually will have an "M" on the panel. The wireless card is about 1 inch by 2 inchs in size and will have a white and bacl wire coming out of it. These are the antenna. Now that you have found the wireless card, remove it, this is done by pushing the little metal tabs on both sides outward the card should kind of spring out. Remove it and then reinsert it. Sometimes the cards get unseated. Once installed reboot the computer. If you dont get any networks still and your card is being recognized you probably have a bad card.