Windows XP Service Pack 3 has been out since April, but it's only now being widely pushed out onto Australian desktops via Windows Update, meaning that pretty much everyone is going to have to deal with it regardless of their geek status. For most people, that means a hefty download (60MB or more) and the usual delays and reboots to have a fully-patched PC. But what if the service pack doesn't install? Read on for our guide to fixing some common SP3 problems.

I've installed SP3 on several XP machines by now, and haven't had problems with most of them -- but today I encountered a machine that flat-out refused to install SP3, even though it had detected that it was available. That process has ended up with Microsoft Support (and still isn't resolved), but there's plenty of steps you can take before you're forced to hit the phones.

Get the basics right

Although SP3 doesn't add much major new functionality (as we've pointed out before), it is a fairly invasive update, so maximise your chances of getting it to install right. Reboot your machine, and close down any applications that launch during startup. Fire up Internet Explorer (Firefox isn't a good choice in this context). If you haven't previously been through the oh-so-annoying Windows validation process, you'll need get that out of the way first by visiting this page and clicking on the 'Validate Windows' button in the top-left corner. Then go to Windows Update and follow the prompts to install SP3.

Troubleshooting steps

Unfortunately, there are plenty of elements that can make SP3 go wrong, from strange hardware drivers to individual hardware products. If you encounter a specific error message pointing to a particular product, try disabling it and attempt a reinstall. If you get a very generic message (like the one at the top of this article), you'll need to try some more general steps.
For no obvious reason, Microsoft has produced a troubleshooting guide to installing SP3 as part of its Knowledge Base, but doesn't actually link to it from the SP3 installation error page. Once you do find it, it proposes five steps: reboot and try again, try install a downloaded version rather than the Windows Update version, disable your antivirus software, make sure Background Intelligent Transfer Service is enabled, and clear the software distribution folder. You can read the details of each step in the support document, but here's two important points to note which it doesn't mention.
Firstly, if you choose to download the standalone SP3 installation rather than using Windows Update (step 2 in Microsoft's list), be aware that it weighs in at 316MB -- a hefty amount if you're on a restricted download limit and an impossible amount if you use dial-up. Microsoft does offer an alternative service where you can order SP3 on a CD, but that costs $14.95 for delivery charges. Even nastier, despite that huge price, delivery takes between 2 to 4 weeks.
Secondly, if you do download the full installer or order the CD, Microsoft telephone support recommends installing it in safe mode, though this isn't mentioned in the Knowledge Base article. (Access Safe Mode by holding down the F8 key during booting.)

Full article @ http://www.lifehacker.com.au/tips/2008/09/01/what_to_do_when_windows_xp_service_pack_3_wont_install.html