shape masks not working

Hi.

I discovered that my shape masks in FCPX (10.2.2) don't work. I can add the masks but the handles just won't respond and therefore the mask can't be moved.

I tried upgrading the OX to El Capitano in the hope that the OS might be a factor but no joy. I can't pin point when this feature stopped working- it was fine a few months ago and of course have only noticed it when I need it. I did upgrade a while ago from 10.2.1 to 10.2.2 - not this may be a factor but this was perhaps one of many possible culprits over the last few months- FCPX froze and had to be forced quit, the mac had a power cut while in use, the 7 year old was playing minecraft on the Mac instead of his iPad when I was away and may have pressed a 'stop masks working' button 😉

I'd be much obliged if anyone can help as it's a great feature when it works.

So do I give out to the 7 year old? Would the OS upgrade have made matters worse, could the power company be at fault? Could the FCPX upgrade be the prime suspect?

I'd appreciate some responses to point me in the correct direction

Thanks

Martin