Activation Issues

Since installing XP-Pro to a new-build system, I have had a peculiar activation problem. XP (Pro, SP-1a) continues to count down the days left to activate the system, yet when I click the icon to begin the process, the resulting window says I'm already activated.

Any ideas why this happens?

I've seen this before, when using a cd key that was taken from the manufacturers installation via a utility like belarc and used with a regular oem cd to re-install.. if you reinstall using the key on the computers sticker it goes away......