I downloaded the latest Ever Note version (22.214.171.12420) and tried installing that (without uninstalling anything) using Windows - which said that it was removing older versions during the process. The new version did the not-responding thing. I thought I'd better check that everything was there on the web-based interface: it was and the visit to the website seemed to please the programme on my laptop because it suddenly started working normally again.
Meanwhile, a message popped up on my 'phone telling me that my Premium subscription was extended in April.
Odd behaviour all round, but it's working again and I've discovered Revo, thanks to this thread.