They're seeing endless, and I mean endless-reboots. Many can't even escape to the relative safety of Windows' Safe mode much less get back to the safe harbor of a previously saved System Restore point. Most of the people experiencing this PC nightmare seem to be running computers with AMD chips.
The core problem though isn't that XP SP3 has a problem with AMD processors. It's that some vendors, and HP is the one that usually gets mentioned, used the same XP image on both their Intel and AMD systems. Usually that's not a problem. It's sloppy workmanship at the factory, but not a show-stopper. Well, until now anyway.
What happens on an AMD system is that when an Intel-only power driver-intelppm.sys--is loaded the newly patched PC throws a fit and locks you into reboot hell.
Well, actually it only seems like reboot hell. You can stop the madness by hitting the F8 key when you first see the black Windows XP screen. Then, on the character-based menu, select "Disable automatic restart on system failure." Chances are I didn't have to tell you that if you've been seeing the reboot cycle for a while. Then select Safe Mode. Once you're there, click on the System button, pick run and follow these instructions from Jesper Johansson, an ex-Microsoftie and now a Windows blogger,
1. Run regedit
2. Click on HKEY_LOCAL_MACHINE
3. From the File menu, select "Load hive"
4. Navigate to %systemdriver%\Windows\System32\Config on the dead system and select the file name System
5. Name it something you can remember, such as "horked"
6. Navigate to horked\ControlSet001\Services\IntelPPM
7. Double click the Start value and set it to 4
8. Repeat steps 6-7 for the other control sets.
10. Send Johansson a thank you note if it works.
Johansson's blog also has advice on fixing other XP SP3 problems. If you're having trouble, be sure to visit it. Of course, what would be best is avoiding this entire mess in the first place. So, if your PC has an AMD CPU, you might consider following the steps above before applying SP3. Now, on my AMD PCs, I never ran into this problem, but if you want to be sure to avoid the reboot recycle, you may want to go ahead and fix your system before hand.
Just be sure not to remove the driver if you have an Intel-based PC. If you remove it then, you'll only give yourself an entirely different major problem. Johansson also gives instructions on how to get out of this mess.
There are other things you should do before installing XP SP3 that will help you avoid other possible upgrade woes. For example, you should turn off any start-up programs, especially anti-virus programs. If you're using the beta of Internet Explorer 8, ditch it. XP SP3 doesn't play with IE 8.
These steps may help, but I'm not as certain of them as I am of the earlier ones I'd mentioned. If you're already running a beta or release candidate of XP SP3, remove them before making the final upgrade. This personally gave me no trouble, but some people have reported trouble when they tried to do it.
Upgrading your drivers before the upgrade may help. Since I always run the latest drivers for my equipment, this wasn't an issue for me. In any case, it's usually a good idea to run the newest drivers to get the best and most secure performance from your equipment so you might as well update them as well so long as you're at it.
Last, but never least, whenever you do a major upgrade on any system, be sure to make a back-up. That way if everything falls apart at least you can restore your data and programs to another PC.