Quick scan with Malwarebytes produced 399 PUPs in the guest account (never had this many before usually 3 or 4 max). Fixed these and rebooted. Disabled guest account.
Then froze while trying to call Chrome from within Pegasus Mail. No response to anything.
Rebooted selected usual user profile, bit of activity, then froze with mouse still mobile on Blue screen (usual wallpaper).
Tried last known configuration that worked but produced the same problem.
Booted into Safe Mode with networking - seemed stable and working at the start. But now calls to Chrome from within Pegasus Mail and via desktop shortcut to Chrome produce no response. IE works OK.
Advice on what next much appreciated.