Internet Is Connected At Full Strength, But Nothing Works?

I got my Macbook Pro in August 2008, and other than having difficulty picking up wireless networks, haven't had any connectivity issues. I've been at home since May 8th, and the wireless here has been working fine--up until a few days ago. Airport says that I am connected at full strength, and diagnostics says that there is nothing wrong with the connection, but nothing can access the internet (safari, firefox, adium, itunes, or updaters). Firefox tells me that there is a network timeout. I have a Linksys router, but I don't think that is the issue as a) three other computers in the house, the xbox 360, and my brother's ipod touch can all access the internet fine; and b)internet from my neighbors or my local coffee shop also don't work. I took it to my boyfriend's house, and it worked fine there where he has a mac network, but that could be a random happenstance as we only tried it once and my internet also started randomly working fine for a while last night. I'm trying to take it in to a genius bar before I leave for school in a week (as there isn't one close to where I'm going), but until then, anyone got any pointers? I've restarted Airport, the computer, the router, and the modem already. Thank you!