Another culprit can be the anti-virus you're using. Even worse, it can be the remains of the anti-virus that was pre-installed in your computer - all brand names have them and some bigger builders as well. I've seen removed McAfee do very strange things starting from preventing Windows from updating.
In such case running the removal tool from the anti-virus manufacturer should (not guaranteed!) take care of what's left of the normal uninstalling procedure.