Recent Mouse Click Response Problem

Within the last month or 2, my Dimension 8300 has stopped accepting quick left mouse clicks - regardless of application.  The click is accepted if I hold the mouse button down longer (2 or 3 times as long as normal, but still less than a second) - as if it were waiting for a poll, rather than responding to an interrupt.  The other buttons (Intellimouse Explorer 4.0 optical, PS2) don't exhibit this problem.

 

I've just spent several hours scanning the Internet - I found another person complaining about the same problem within the last few weeks, but no suggestions for fixing it.  I have the latest Intellimouse software and XP (SP2) drivers.

 

Any ideas?

 

Jim Weisz