I'm willing to try voodoo at this stage.
Sorry mate, we tried that over a year ago and it still didn't work. I've even promised the soul of my first born to the devil
I'm not sure how it would be able to obtain an IP address but not connect to the internet (if that is the case). It's wired directly to the router so not exactly a problem with WiFi or MAC Filters etc.
duff DNS or Gateway settings would still get you an IP but no routing of traffic. Try static and make sure both DNS and Gateway are set to your routers ip or use 3rd party DNS like Google. Simple stuff I know but what the heck!