Re:This happened to me this past weekend (Score 1)

Happened to me a couple of months ago, Vista Ultimate OEM that I purchased and installed on a home-built PC. I think it was a WIFI driver update from Windows Update that caused it. It gave me about 60 days to re-activate. I left it until Windows went into reduced functionality mode before calling MS, hoping it would 'fix itself' and dreading calling the Indian Call Centre (from the UK). When I had to call, the Indian guy was extremely polite, perfectly understandable, and the process was painless. While I wish the driver update hadn't deactivated my Vista in the first place, I was impressed with how easy it was to get it re-activated. Kudos Microsoft support, YMMV.