Try updating the NIC driver on your PC, and seeing if that makes a difference.
Set your connection as "nailed up" in the router.
If your hardware has automatic cable recognition it'd pay to ensure you are not inadvertently using a crossover LAN cable. It would pay to try a fresh cable anyway.
You could also check your DNS servers are not set differently in the adapter and the router.
Flushing your IP cache wouldn't hurt either