had to do a repair I installation. )
I recognized that all MICROSOFT software was simply gone on the C-partition.
Sounds like you missed a step of an ISO Upgrade Repair and accidentally did a full install with it.
Just to put you in the picture what Microsoft regard a repair installation retaining software and settings.
I myself managed to get out of the infernal reboot dilemma by clearing out all temp files, doing a complete disk cleanup including system files (3 GB accumulated!) plus deleting files from Windows\SoftwareDistribution\Download. Then all I had to do was double-click the downloaded.... msu file and installation went like a charm. What I did was probably crude, but it worked.
Another chap, same problem as of all us here, used the repair method and found that of all things, Microsoft managed to corrupt Microsoft Office installation. So much for retaining software!