I think we would need more info to try and help you. Try going to Windows Update and "view installation history" and give us a clue as to exactly which update you are having the problem with. It might be a coincidence also or you might have gotten some spyware since the time you installed SP2.
I have previously installed sp2 with no problems. However, on October 14 I downloaded a critical update to SP2 from Microsoft update. Around that time, everytime I restart or boot up pc, I get the Windows Product Activation. It requires me to activate (or I can't get past the welcome screen), which I do (successfully-as always)and can move on with no problems. However, next time I restart or reboot..again it wants me to activate Windows. I am currently working with the Research department at Microsoft, but they have yet to come up with a solution. I cannot uninstall this update without removing the entire SP2 update..anyone else with this problem, or can help?