Therein may lie your problem. Some ISP's, especially cable, register the MAC address of the PC that was originally setup on their network and only allow that MAC address to connect to their network. Because of this, most routers have "MAC address cloning". Just get the MAC address of the network device on your PC and plug it into the "MAC address clone" spot in your router software and viola, it'll connect to the internet again.

That MAY be the problem. Not sure, but it's definitely worth a try.