Multiple Mouse Clicks Required

I am running XP Home SP2. Recently File Explorer, Internet Explorer and
Firefox have begun requiring multiple (usually two) mouse clicks to open or
expand a folder or link. In File Explorer I can sit on a bookmark folder and
consistently every other click will expand or compress the bookmark folder.
It does not depend on the speed of the click (I can wait 10 seconds between
the clicks and still every other click will be effective). In IE7 two clicks
will often be required to open a URL link. This problem occurs both with a
wired and wireless USB mouse. Help Please!!!