First off, I've spent a week searching for a solution to this so if I've missed something obvious I apologize.
My xbox has been connected as a media center extender to this computer and router combination for several months now. The router is a Buffalo WZR-HP-G300NH. Earlier this week the media center extender was having trouble playing back video. After a restart of the computer the extender was no longer connected.
When I try to add a new extender I get the message "Cannot add extender". Microsoft says to enable upnp and multicast. Check. Reflashed firmware to dd-wrt. No luck. Flash back to buffalo firmware. No luck. Try an old Linksys WRT54GL I have lying around. No Luck.
The event logger has this error: "Media Center Extender Setup failed as the Extender was detected on the network but the UPnP search for the Extender failed (timed out after 20000ms)." Event ID: 538
Now I've done everything I could find about enabling network discovery, allowing anything to access media and such. Network and sharing is set pretty much wide open. I've also tried switching between home and work networks.
With that said, I decided to check and see what updates have been installed. It turns out that an update was applied on the day I started having problems. It says it cannot be uninstalled. Description of the Windows 7 and Windows Server 2008 R2 installation software feature update
Note: I do not have system restore points. Small SSD and didn't take the time to figure out how to save them elsewhere.
So that's all the information I have. I've convinced myself it's not the router through the steps described above and that it's something to do with the computer. Help?