I have re-installed the Win 10 and all of the apps we have added. Firefox, Libre Office, Money, Fitbit and a few PC maintenance things. The BT is still dead but at least the Fitbit app is now showing this rather than going through the expected Finding device - connecting - synching reporting without actually doing any of it. Took a while getting everything set up as it was before. Just need to get the FILs router code back in, at his.
The question of built in or external BT dongle has reminded me that I have a USB - BT dongle I could try if I can find the driver(s) for it. Thanks Nutloose.
Rans6........................