I can't install any Windows XP upgrades, including Service Pack 3, after the following sequence of events:
1. I used SpyBot to check for spyware. It found 8 objects and removed them.
2. The next time I turned on my computer, it immediately logged off my user name each time I logged on.
3. An IT pro I know said this was a known prank spyware, and that the only way to recover is to rebuild Windows.
4. I reinstalled Windows using the Repair current Installation feature (not the Repair Console). It reinstalled XP up to Service Pack 2.
5. I then was able to install Service Pack 3 and the upgrades that follow it.
6. A week later, three later upgrades reported that they could not be installed due to a "problem with my computer".
7. I ran SpyBot again, figuring that some spyware was causing the problem. It found 4 of the same items it found the earlier time. One had the string "Microsoft Windows Security" in it.
8. I got the log off after logging on problem again.
9. I reinstalled XP up to SP2 from the system disks again.
10 Now it won't let me install SP3 and later upgrades. The only error message is "Not installed".
11. Microsoft Auto Update repeatedly was trying and failing to install these. I shut it off, so I could get some work done.
12. I did a full hard disk file system and surface scan, with no errors.
13. My IT friend told me to use Windows Defender instead of Spybot, and that Spybot might be changing a setting that is not supposed to be changed. I installed Windows Defender. Windows defender finds no problems, but has an error message when I try to download updated lists.
WHAT'S GOING ON?