Mouse clicks do not register

Question

Over the past few weeks for no apparent reason mouse clicks will stop working on my Mac Pro. Generally speaking, clicking will work in the dock, system menu bar and sometimes a click on a background window of another application will bring to to the front. At other times clicking anywhere has zero effect.
The mouse moves around the screen fine otherwise. I generally use an Apple wireless trackpad but once this problem occurs it doesn't matter what input device I use - a wired mouse, my wireless Wacom tablet, etc. - the problem remains. I can tab around within an application, fill in text fields or open files using the keyboard. But even using screen share and taking control of the desktop from my laptop the problem remains: clicking of any kind does not work. So it's not the input devices or their connections.
On occasion I will hit command-option escape and force quit all applications and restart the finder and that will work. Other times not.The system remains responsive - no spinning beachballs etc. In the end I'm forced to restart the computer and everything returns to normal.
Whats-a-going-on? Any ideas?

Answer 1

Sorry, missed that...
My point remains the same: if your hard-wired devices are known good, then you have a intermittent problem that resides either in the OS or in hardware.  The nexts step are along the lines of reseating all the boards, running hardware tests, etc. to try to determine if it's hardware or software before re-installing the operating system.
The other option is to take it to an Apple qualified service guy. If you do that, I'd look for a Mac Pro specialist (someone who works on pro video or audio systems, etc) since most Apple Stores are mostly for iPads, not serious hardware.
Good luck