This is a problem I have seen a lot of the past few days. It has affected Windows Vista and Windows XP; however, with Windows Vista it is able to repair itself with the built-in startup repair tool. Windows XP users have to call somebody like me to fix it. The security update is labeled as MS10-015 and listed under the Microsoft knowledge base article 977165. To repair it, you'll need a Windows CD or DVD.

If you happen to have a Windows XP CD, follow these instructions:

• Boot from the CD.
• When prompted to set up Windows XP, press R to start the repair command prompt. After a few seconds, choose one of the Windows installations listed, ideally the one which is on the hard drive of your Windows XP installation which is usually C:\Windows. Enter your Administrator password which, for most people, is blank.
• Type "CD $ntuninstallkb977165$" (it does not matter if you use upper-case or lower-case).
• Type "CD spuninst".
• Type "batch spuninst.txt"
• Type "exit" to reboot and that should fix you up.

If you happen to have a Windows Vista or Windows 7 DVD and want to repair Windows XP, follow these instructions.

• Boot from the DVD.
• When prompted to set up Windows, click on the recovery tools listed at the bottom on the window. Follow the on-screen prompts until you see a window with several options, the last being a Command Prompt. You want to click on the Command Prompt option.
• Type the hard drive letter with the Windows XP installation on it and press enter. It is probably C: but it may be any letter at all. If in doubt, keep trying successive letters from C:
• Type "CD \Windows".
• Type "CD $ntuninstallkb977165$".
• Type "CD spuninst".
• Type "copy spuninst.txt spuninst.bat".
• Type "spuninst.bat".
• And reboot your computer.

If you have Windows Vista or Windows 7, just use the built-in startup repair to fix this problem.