Try the fixes here: If LW Will Not Connect
Start off by changing listening port

Also, check that the Windows firewall's off & that McAfee's allowing LW. There's more info about configuring McAfee here: Port Forwarding for the McAfee Security Center

Many schools don't allow p2p use. You should check with your school to see whether they do or not. If there's no problem with the school allowing you to use LW, ask around & see if other people can use it without a problem.

Do you have an external modem/router that plugs into your computer, or that you connect to wirelessly (might be in another room at home)? If you do then we'll need to know the brand & model.