You may be having software compatablity issues with SP2. First make sure the software you are running is compatable with SP2. If it isn't try to get your computer to run long enough to download an update from the software's manufacturer.
If you are still having trouble, you may have to restore your XP system files with the XP source disk. With the disk in the drive, press a key at bootup to boot from the CD. Use the option to install XP and then choose the option to repair system files. This will repair your system files and should bring your computer to a working state. You will loose SP1 and SP2 during that process. Now, turn your automatic updates off. You can do this in the control panel by clicking SYSTEM and then clicking AUTOMATIC UPDATES. Now navigate to the Microsoft update site, or just click UPDATE WINDOWS from the tools menu in IE. Download just the updates you need avoiding SP2.
Hope this helps