For a few weeks I've had problems with my 64-bit Windows 7 system, where left mouse clicks wouldn't "take" randomly. Sometimes I had to click a few times, sometimes I had to hold the button down, really: maddening. It appeared to be independent of application.
Searching the interwebs showed this was not an uncommon problem, with suggestions pointing to changing USB bus options ("don't turn off to save power"), updating drivers, and the like. None made any difference.
One set of suggestions revolved around changing one's mouse, but it was raised by folks with more exotic, specialty/gaming mice, and since I have a plain vanilla Dell mouse that I've been using for years, I just didn't see how this could be it.
It was; replacing the mouse with one from Microsoft made the problem go away.