canvas non-responsive

Hello,

In Motion 5.2, which has always worked well in the past, I suddenly find myself with a non-responsive canvas. I cannot do even the most basic tasks, like resize an object, move an object, create anchor points, etc. Each of these features and many more are completely non-responsive.

Yes, I've reset all my preferences. Yes, I've uninstalled and re-installed (three times). Yes, I've tried previously known-working media. Even gone so far as to reset PRAM, etc.

I can't help but feel like there's some switch that has somehow been flipped that precludes the use of all these most basic features and I don't know what it is or where it might be.

Thanks for any thoughts.