The problem would be there if you have used torrent. if you try to stop or close the application or try to delete the torrent exe, then it will be happening. i used the torrent for downloading older movies, thro torrent, which has peers and seers, and one fine day i deleted the application. Normally as would be, i restarted the computer, my modem light all goes and everything normal, but the ethernet blinking green lilght would not glow. So, you would not get the connection. The computer to computer connection totally deletes the dns and you will not get internet access.
i do not know, whether it is because of this. This may be one of the reason, which i faced.