Have ye tried rebooting the router?
I have the same router and sometimes it needs a reboot although it's usually the wireless side which stops working for me.
After you reboot the router, reboot your PC.
I have unplugged both cable modem and router from power and left them off for a few minutes without any difference, besides my laptop is running off the router so it is my desktop.
I have also changed cables to no avail.