Windows 7: Computer keeps disappearing from Xbox 360 video library

Hey all. Just built a new system. This isn't really the most pressing of issues, but I'm curious as to why it's happening.
I set my PC up to the home network, added video folders to the media center library and all that jazz, and everything seems to work just fine. Only issue is, after some time of not using it, when I go to watch something on the Xbox, my PC doesn't show up. It's set not to fall asleep, so it should be actively showing up on the network. I go into my room and reset it and it shows up just fine after that. This has happened more than once.

Any ideas as to why this is the case. Shouldn't it always be there if it's not asleep?

It's running Windows 7 Ultimate x64. Let me know it I've left out any other relevant info.



Thanks!

In device manager under network adaptor "properties" then "power management" tab, try unchecking the option to turn off this device to save power.