Activation undone?

Purchased server perhaps a year ago. Came preinstalled with 2k3ee and has
been running just fine and dandy all this time.

This afternoon, I guess the server received a Windows update that has
"killed" it (for all intents and purposes).

Now, whenever I attempt to log in, I get the warning:

This copy of Windows must be activated with Microsoft before you can
continue. You cannot log on until you activate Windows.
Do you want to activate Windows now?

To shut down the computer, click Cancel.
[Yes] [No] [Cancel]

So...

If I click Cancel, the computer shuts down. If I click No, the computer
returns to the "CTRL-ALT-DEL" screen. If I click Yes, the computer proceeds
to the Windows Product Activation screen and states:

Windows is already activated. Click OK to exit.

However, when I click OK to exit, I'm returned to the "CTRL-ALT-DEL" screen.

Any ideas on how this happened and how I can correct the problem?

Thanx.