Associated/Not Associated

I have a Dell Inspirn B120 and up to a couple of days ago was able to
get on the internet via local wireless networks in my area. Now it is
saying it is connected but I can't actually get online...The only thing
I see that is different is that it's saying the link status is 'not
associated' now. I don't know how to change that. Also, it's saying my
firewall isn't turned on now but when I check it it says it is. I am
very new to all this and would appreciate any help at all. Thanks.