Yes, Josie, it's encouraging to know that I'm not alone. If you Goggle "Lost left mouse click" then filter the results such as Firefox and Yahoo it leaves a few thousand trails to follow.

I posted the problem on majorgeeks.com where there are hundreds of troubleshooters and still no solution. Be assured that I will share whatever I find out.

True, a deep scan followed by a boot-time scan yielded nada, zilch.

Amazingly, the exact configuration on my Dynavox speech synthesis device (Win 7/32) is still working flawlessly.

Pulling me wee Oyrish 'air oot in the Southern Provinces.