Cannot move or resize windows with mouse

[levbob]

Hi,
Relatively new to Mint - been using it for past year as secondary system (still stuck on Win 10 because reply on Dragon).

Currently running Mint 19 with Cinnamon (3.8.9) on a Dell Vostro with i5 cpu. AMD/ATI graphics card with 2 screens.

Have quite suddenly found that I can no longer move (or resize) any windows using the mouse. I do get a tiny bit of movement when I try but just a few mm. Don't recall making any tweaks that could be responsible. Have done some research and find that issues with switching workspaces may have an impact - but that's not something I've been using.
Have also been reading about using Ctrl-F7 and other strange combinations. Never used them in the past and they certainly aren't working now.

Any suggestions?
Bob