DirecTV does not officially support using the ethernet connection on the back of the box. I will say it should work fine so long as you only have one box in the home, but using a hardwired ethernet cable will disable the internal deca and may cause multiroom viewing issues. I would recommend having a broadband deca installed on your system to provide a hardwired connection.
Thus being said, to accomplish what you are asking, go in the menu, then in the settings, then to network settings, then click on restore defaults. after that runs, click on repeat network setup. It should come up with an 88 code automatically, if it doesnt something went wrong. Once you get your 88 code, reset your box manually with the red button just for good measures and youll be good to go. Again please note we will not support this method of connecting to the internet.