Check to make sure that the port on the router didn't die on you. Plug the computer into a different one.
Check to make sure the cable didn't get pinched and cut or sliced... cats/dogs sometimes chew things.
Make sure the cable is still plugged tightly into the back of the computer.
See if your laptop will work if you turn off the wireless and plug it in with the same cable your trying to use for the desktop.
Make sure the network card in the computer didn't die. Does it have lights flickering or at least coming on when you plug in the cable?
Does the computer say anything about network cable unplugged or limited or no connectivity?