Wireless Connection Problem-HELP

So I have the Macbook that was released around Oct 2009, i've had it less than a year. It was working great, then about an hour later, It said I could not connect to a wireless connection, and when I open a page it says i'm not connected to the internet. My wireless modem is working fine, because the other laptops in the house are working fine. When i connect my macbook directly to the modem, it works fine. I've tried updating everything, and still no luck.
does anyone know what I can do to fix this?!

 

Yes, I've tried multiple times..I even took it to school to try and connect to their Wireless Network (which i had no problem connecting to before) but that didn't work either.