Have you downloaded the latest drivers for the router? just incase they are
here
Have you tried another cable between the STB and router?
Can you connect through USB from router to computer or STB and router? Ikow USB sucks but if it works then its the cables at fault.
What RJ45 cable are you using between the PC and the router?
If crossover try a straight one if the other way around still try another between the router and pc
Can you borrow another router from a friend to see if you can connect with that one?