I can only give very general advice as WiFi problems can range from being very basic to complex. To get a better chance of fixing the problem you need to try to indentify the problem – be as specific as possible; “It doesn’t work” is very general 🙂
If you can’t connect to the WiFi Access Point:–
1. Check if other laptops are having the same problem.
2. Check that the WiFi is actually switched on (ok thats very basic but often overlooked)
3. Check the signal strength, if it’s poor try moving to find a stronger signal.
4. Check to see if you can see any other Wireless Networks showing up in Network Connections
5. Check to see if you can connect to any other WiFi Access Points.
6. Check to see if there are any extra security measures in place e.g. MAC Filtering
7. Check to see if DHCP is enabled on the WiFi router (Access Point)
If you do get a connection to your WiFi router but it keeps dropping or the signal keeps varying from very week to strong:–
1. Check for interferance from things like Wireless door bells, Baby monitors, Microwaves etc (WiFi is a radio signal and is subject to the same type of interferances)
2. Install a WiFi scanner such as inSSIDer or Netstumbler to check what other WiFi networks are in range and what channel they are using. Quite often you will need to change the channel of your WiFi in the config pages so that you get less interference from other networks. Most Wifi routers have a default channel set and if several of your neighbours have the same router, you have a very good chance of getting interference but that will depend on how strong your neighbours signal is in your house.
Although WiFi is convenient, consider the homeplug/Powerline alternative