I have seen a thread on this today, and followed the suggestions therein.  namely to Open the Font Book application, Select all fonts, Validate, I then removed the fonts that were labelled as not working, to no avail.  I then tried the SAFE BOOT and this succeeded and both Excel and Word were back to normal.  

However 20 minutes later, after closing and opening Excel and Word again, I am back to square one.

Any help would be greatly appreciated