Hyperlinks in Excel suddenly stopped working - help!!

Hi, my hyperlinks in Excel suddenly stopped working today. MS support tried for hours to fix it and failed, including a system restore. Equally, URLs embedded in Word docs suddenly don't work either. Yesterday I downloaded 4 new internet browsers, maybe that caused it, but I deleted them and it made no difference.

PC, Windows 10. 

I get the message "Your organization's policies are preventing us from completing this action for you. For more info, please contact your help desk."

It's my private PC, not connected to a network, the files are not shared. I've been using the same excel file for 8 years and never had a problem with it. Firefox was and remains my default browser.

When I did some research earlier people wrote about changing something in the registry. (1) I haven't a clue how to do that, and (2) there were various propositions so I don't know which one would be the right one. I'm not a tech person at all, I just got sent here by MS support because they couldn't solve the problem.

HELP!!!