Sometimes the problem is the router you're using. Belkin routers has known compatibility issues with Macs, although Belkin tech support will deny any issues. If you're using a wireless card, sometimes your location is the problem. You might be too far away from a tower. Or you might live in an apartment on a high floor or there are too many trees blocking your signal. You might need a signal booster for your wireless card. I hear Verizon makes one.