EXPLORER Not Responding

With increasing frequency I'm encountering frozen screen which, when Ctrl/Alt/Delete, shows Explorer Not Responding. Occasionally it will be another, such as Msnmgr, etc.
After End Task screen unfreezes and I can continue whatever I was doing, but various lower task bar icons have disappeared. Sometimes a bit later the freeze will reappear with a different site Not Responding.

I have been told existence of se.dll may contribute to the problem, but ran updated Spybot S&D and result, no problems.

Appreciate help, recognizing I am a computer novice (and even that may be an exaggeration).
Thank you. RO