No more double clickability!

Mac OS X.5
Power PC (non-Intel) G5
Recently, my mouse stopped working. Temporarily, I used a mini mouse, but it was erratic. Then, I bought a new Logitech mouse, but double clicking does nothing, nada, zilch. I’ve uninstalled and reinstalled the software. I contacted Logitech support. Nothing’s worked. I’ve decided to return that mouse. In the meantime, I went back to my original single-button mouse. Talk about going backwards in time! But, it does nothing when I double click, now, too. What could possibly be the culprit??? Thanks for your help/suggestions!