This post is "for your Information", rather than seeking help;
For the third time now I've experienced, out of the blue, "Opera not responding" a couple of seconds after opening.
Checking resources via Task Manager, shows High CPU & Memory usage and Very High Power.
This last time, I downloaded the latest version and upgraded, to no effect.
Correlation with my vague memories of the past, I think in each case, the cause has been the same.
Win10 64 bit has updated in the background, silently and without my knowledge, and has been sitting awaiting a re-start.
Even at this point, before the restart, Opera freezes, just giving the options to wait or close, (if indeed this popup appears at all; sometimes I need to use Task Manager to End Task). After the re-start, there is no improvement; and changing various Opera, or Windows, settings makes no difference.
I've now found that just allowing Opera to Wait, it eventually kicks back into life. The PC can be used with a different browser whilst you're waiting, and functions normally with other programs; albeit a little slower.
N.B. don't be impatient, I've had to leave the PC turned on, with Opera consuming lots of resources, for upwards of 3 hours, and once overnight. It does however eventually sort itself out.