It is surprising how difficult some “simple” problems can be.
When trying to install PostgreSQL, the system was complaining because the “postgres” service account already exists (and I didn’t know the password any more, probably leftover from long ago). Anyway, the “easy” solution would be to delete that service account to that it can be created anew, using a freshly chosen password.
Using the command line type
net user /delete postgres
That’s it. Now if google could have told me that immediately, then it would have saved me two hours today.