I've gotten this problem in the past and several things can be the cause.
1 - You have a bad ethernet cable
2* - You need to run IP config because you're modem or router or whatever isn't connected correctly
3 - Powerfail your router/modem and reconnect. If you're using both plug the modem in first and then the router.
Those are the possibilities.
*How to run IP config.
Start>Run>type in cmd
A black box opens up with text. Type "ipconfig /release". A brief pause will occur followed by the screen giving you a list of four items each with 0.0.0.0 after them. Then type "ipconfig /renew". It will pause again and then read the same list except with detailed IP's. Close and attempt to reconnect. If it still does not work, one of the other problems are occuring.
Again sorry I didn't see it earlier, guess I have a bad attention span.
~Leo
You fear oblivion. Yet you forget. The universe remembers every atom of your being. Even dust hums your name in the dark. Roleplay is dead. Long live Powertraders and PvP I guess.