It is the media share server responsibility to provide the network information/connection to the Directv equipment.
Either restart the PC or the media server software you are running on the PC to get the Directv equipment to see it again. The media server software can be TVersity, WMP11, Nero, or any number of media server software choices.
Your PC or media server software could be going into a sleep state or something similar to that and creating this problem.