Windows 7 Awful networking issues

I've got 1 windows 7 media center box (32 bit), my laptop (win 7 64 bit), my girlfriends laptop (Win 7 64 bit), and an xbox 360. The media center box used to be XP I upgraded to windows 7 and all was well. I was able to connect to and stream movies from the media center to the xbox. I was able to connect to a file share on the media center box from my laptop. However, my girlfriends laptop would request a login when doing the same operation. Some reason midway through a movie it just stopped streaming. In trying to track down this issue the media center box has completely disappeared from the network. The media center pc can connect to the internet. My laptop and the xbox 360 can't connect to the media center or verify that it is on the network. I have a Linksys E1000 router. I've been reading forums and looking around the internet. I've spent way too much time on this problem, and it's getting very frustrating.

I'd be very great-full for any help