Can't click on Desktop or Taskbar without CTRL-ALT-DEL

[Guest]

I have Windows XP SP2 on an Intel Celeron 1.3 GHz system. Whenever I start
the computer, and every few minutes after that, the system will not respond
to mouse clicks or mouseovers on the Desktop or Taskbar, though it will
respond to clicks and mouseovers within an already running application. It
will start responding again only if CTRL-ALT-DEL is pressed to bring up the
Task Manager. I've run several virus and spyware scans with products from
different companies and found nothing. I've also run SystemSuite 5's
Registry Fixer and removed all junk entries, but without effect.

 

[Guest]

Also, the problem sometimes happens in reverse, where the computer won't
respond within an application window, but will respond on the Desktop or
Taskbar.