Computer can find router but no internet?

Alright, I've been using my computer for a little over a year now and on the 21st of december, I believe it was, the internet just stopped working.

I have a Linksys router "Model # - WRT54G2 V1.5" and everything connects fine to it (ipods, xbox's, laptops, etc...) and gains all those access to the internet but not my computer. It'll find the router and say it has excellent connection but no internet access.

At first I thought it was my usb network adapter so I went out and upgraded to an "AE1000" (also linksys). But this didn't help at all.

I've been through tech support numerous times and have been working on this for almost a month now! I need help please! And thanks for reading, I really appreciate it.

Sorry, I forgot to include this: my computer is wirelessly connected to this one, this is the computer with the router, it still has internet.

Can nobody on here help??