For best performance and least problems, enter msconfig>Startup and uncheck everything except your AV and gadgets/stickies if you use them.
After several reboots, enter msconfig>Services, Hide all MS Services and do the same.
Check back periodically that nothing writes itself back in. If so turn it off in its Program Preferences or Uninstall it. Freeloaders hog your RAM/CPU, slow startup and can spy on you.
You now have a clean boot.