The PC of a friend, visited his house got activated there, then days after moving the PC back to his friends house it got deactivated.
M$ watching IP address and saw the change caused it?
I have had my Windows go not registered, I have cable and my IP address will change and so I suspect this is exactly what happened to your buddy.
Try this thread: Activate Windows 7 Online
I have to use this: http://www.microsoft.com/genuine/
If I download the .exe and run it, it fails.
M$ is so bloody greedy this whole activation thing is proof, they are spending millions on tech support for just this and outsourcing tech support to all over the place and it's downright painful with the language gap, it's been a mixed bag when I needed it.