You try to do the right thing by setting your PC to update Windows automatically, only to be stopped in your tracks by some error message or--more likely--a hung browser. Usually there's a simple explanation for the update hiccup. But not always. The steps below for resuscitating a stalled Windows update begin with the simplest solution and end with the trickiest.
Make sure you're logged in an administrator account. To find out if your current account has administrator privileges, click Start > Control Panel > User Accounts (in Vista's standard Control Panel view, click User Accounts and Family Safety, and then choose User Accounts). If the account you're currently using isn't labeled "Computer administrator" in XP, or "Administrator" in Vista, log into an administrator account and try the automatic update again.
Temporarily disable your security software. Overzealous firewalls and antivirus programs may inadvertently block Windows Update from downloading and installing necessary OS patches. Right-click the program's icon in your system tray and choose Exit or Disable (you may have to open the program's management console and close it from there).
Unfortunately, the only way to disable some security programs, such as Symantec's Norton 360, is to open Task Manager and disable them there. To do so, press Ctrl-Alt-Delete, click the Processes tab, find and select the process for the program (it likely uses a variation of the product's name), and click End Process. The process will restart automatically the next time Windows loads, or restart it manually by clicking its Start menu shortcut to reopen it.
Check Microsoft's update-troubleshooting site. The first time I visited the Windows Update Troubleshooter, I expected to find a great tool that automatically scanned my PC and fixed whatever was blocking Windows from updating. Instead I opened a page with a long list of links to articles intended to help you figure out the problem on your own. You can find much the same information by copying the error code that appears when Windows Update fails and pasting it into your favorite Web search engine to discover information about it, and possible a solution.
Run the Windows Update Fix batch file. The CastleCopsWiki offers a downloadable batch file that automatically addresses many of the causes for a stalled update. Use it by unzipping the download file and double-clicking the file named WUFix.bat. This is far from a guaranteed fix for update woes, but if everything else has failed to resolve the problem, it's worth a try.
Tomorrow: the best alternatives to Adobe Acrobat.