Connected to network but can't connect to internet

I'm running OS X 10.4.11. I've never had a problem connecting to the internet until yesterday. It looks like I am connected to my wireless network but when I try to open the internet it says that my computer isn't connected to the internet.

When I run Network Diagnostics, I get green lights on Airport and Airport settings, yellow on Network settins and Red on ISP, Internet and Server. I've reset my router several times. My XBOX Live is working just fine.

I also tried connecting to the internet at my office with no success. Any ideas what could be the problem?

Thanks.
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Delete the wireless network connection on the computer and reconnect.

By that do you mean disconnect from that network? I've done that several times. I'm not sure exactly what you mean by that. Thanks for your help.

I am not on my mac, so I cant tell you exactly what settings interface to change, but you want to get to your main network settings panel and remove (not disconnect) all wireless connections.

Maybe someone will be able to tell you the exact settings page to do that.