I "think" I may have a faulty cable from my SignaLink unit to my FT817. I shall get a new one to see if this makes it better. The PC sees the SignaLink unit, I have TX enabled, and the FT817 works fine on USB so the FT817 PA is OK. In days gone by I'd have tried to fix the lead, but not these days as I am still unable to manage fine motor skills as a result of my stroke. I do not think this is a Windows 10 issue as I can hear the TX if I select the PC's own speakers.
Luckily I am still able to be on 10m WSPR with the stand alone beacon.
Knowing my luck 6m will be wide open across the Atlantic these next few days!
UPDATE 0948z: New lead ordered from W and S. Should be here later this week.