Tells me "Server Not Found" when all other computers work?

[Polywater]

Hi. Today i tried to get on firefox and something weird happend. it told me "server not found" it has never done this before and now i dont know how to get back on. its been like that for 3 days. but whats really annoying is that my moms hp laptop and my brothers MAC laptop has the internet. mines the only one in the house that doesn't. and it shows that i am connected to the internet and that i have a strong full signal! please help?

Thanks

 

[Shikatex]

Same problem

Having nearly the same Problem except my dad did something to the airport extreme I ge Internet at school but not at home I need his airport express or whatever it's called password but I can't reset the password cause he'd kill me