I have a Windows XP system that has been running fine for a long time. However, yesterday I rebooted it for the first time in a while, and when it came back up, it did not let me log in to the system and came up with a box saying:
Windows Product Activation This copy of Windows must be activated with Microsoft before you can log on. Do you want to activate Windows now?
Because the system does not have any internet access, I tried to run through the activation system by phone, but the key was rejected. I then rebooted the system again. It came up normally straight away - no activation screen, no trouble.
I have seen this on other computers before, but I have never found out why it happens. Does anyone know what could be causing this?