In some cases, various software updates applied through Windows Update will hang partway through their installation processes under Windows Vista. In some cases, the hang will occur right before the system is to be restarted, forcing users to manually shut down their computers then power on again. However, the system may not recognize that the updates were applied, and prompt the user to install them again after the forced restart.
Eliminate the hangs The first step in fixing this issue is to eliminate the existing hangs. Usually these hangs are caused by the presence of anti-virus software or other third-party protection mechanisms, such as Zone Alarm or AVG. Try temporarily disabling these programs (in some cases you may need to uninstall them). After disabling or eliminating this software, reset your Windows Firewall to default settings (open the control panel, click on the Windows Firewall icon, click on the Advanced tab and then click the Restore Defaults button.)
Next, re-attempt the update(s).
Forcing a stalled update: safe mode If you are already in the middle of a hung update (your system has been manually restarted and is prompting for the update again), try rebooting your system in safe mode by pressing the F8 key while the computer is starting up. Immediately after booting in safe mode, boot into normal mode again. This may allow the update to apply.