Thank you for swift reply. I did have Components 3.0.0-beta3 and I had cleared cache etc-but I restarted all services and cleared the cache and I seem to be back in.
However I do get an error in the log "Warning: file_get_contents(themes/custom/bob_radix/build/js/main.script.js): Failed to open stream: No such file or directory in Drupal\Core\Asset\JsOptimizer->optimize() (line 25 of C:\wamp64\www_d10\public_html\core\lib\Drupal\Core\Asset\JsOptimizer.php) ".
This seems to be because there is no directory 'themes/custom/bob_radix/build' which there was in my version D9. It seems to be the same as 'themes\custom\bob_radix\src'.
I could just create a 'build' directory or ignore the warning? - or do you have to run 'npm install dev' or something to create that?