I had a problem a while back with the media center extender in windows 7. I could create a verification code, but the Xbox wouldn't see the PC after setting up the code and trying to connect to it. I had just formatted the PC and it had been set up before I had done this, and worked just fine. I had a list at one point of a variety of tips and 'fixes'. There were twenty six of these and none of them worked. I spent a week trying to figure this out.
It seemed as though a lot of people were having the same problem after reading posts in many different forums, so I thought I would go ahead and post what I did to fix this. I removed all of my network connections from the windows 7 home group. That's it. All was gravy after and since. I did this after remembering that I didn't bother adding it to a home group when I set the computer up with my network. I hope if anyone is having this migraine inducing problem, that this helps.