MacBook won't connect to the internet!!!

I recently switch wireless service at home to At&t.

Since, my computer "connects" to my network, accepts my password, and shows full signal, but when I open Safari, or any other app that requires internet, I just get the "failed to open page because you are not connected to the internet" page.

My roommates connect to use our wireless network with their PC's just fine, and my Mac connects to other wireless service at school and work and works just fine.

I have been on the phone with At&t many times trying to troubleshoot and fix the problem. No success.

Apple charged me $49 to talk to them, with no success.

I HAVE ALREADY TRIED RESTARTING both my Mac and my router, I have reset the router, I have restored original settings in both Safari and my router, I have tried removing the security from our network in order to connect without a password, I have tried re-configuring the router to work with Macs....all no success.

I am very frustrated with the situation as I, like most people, require internet access for both school and work.

Any help, tips, or advice on the situation would be grateful.

Thank you.