Vista - Vista 64 Mouse/Focus Issue

Hi,

I'm having a problem using Windows Vista 64 bit. Occasionally every one
minute to an hour, my mouse will not click anything on the screen anymore.
This happens in both Windows and in games. The only way to rectify the issue
is to ctrl-alt-delete, and choose to open the task manager. From this point,
I am able to click again.

I believe that explorer or the active game is losing focus, to an invisible
application. I have tried using three different mice, fully reinstalled
mouse drivers (and any hidden mouse drivers), removed any running software or
processes which were active.

I'm not quite sure where to go from here, and I'm practically ready to
reinstall Windows if I cannot find a solution.

Any suggestions would be greatly appreciated. Thanks in advance.