Left click not working, first with buttons on laptop and trackpad tap-to-click function, a year later with external mouse.

About a year ago, my Thinkpad lost the ability to left click with it's built in functions. This happened totally out of the blue. The left click buttons both above and below the trackpad did nothing, and tap-to-click on the trackpad additionally did not work. Right click functionality was unimpaired. This I found to be good evidence that the issue is at the software level as opposed to hardware. Further, when I selected the option to swap left and right click, I was able to left click, but not right click. I read about similar problems people had and took the advice of uninstalling and reinstalling the appropriate drivers, which had no effect on the problem. After trying a number of methods with no results, I decided to just use a mouse, since that restored my ability to click and use the computer normally. It was a little annoying, but it worked, so I have been doing that for about a year, bringing my mosue with me wherever I brought my laptop. Then, about a week ago, when I attempted to use my computer, the left click on the MOUSE no longer worked. I was getting the same symptom but in the mouse in addition to built in buttons. Now without a good way to navigate my computer, I have been using my other one instead and haven't done any troubleshooting. Are there any ideas of what could be causing this problem and what I may be able to do to fix it? Should I go ahead and wipe the computer and start fresh?

It's a Thinkpad 510 (I think, it's not with me right now), running Windows 7 professional.