Maybe there's some info in Event Viewer which might serve to figure out why it won't install.
- So in Event Viewer expand Windows logs ---> Setup
- Right click Setup ---> Click Filter current log.
- Change Anytime to something which reflects the last time you tried to install KB3146723.
- Checkmark: Warning.
- In Event sources, checkmark WUSA in the list.
- Click OK.
Theoretically you should only see log files for KB3146723 since everything else has been installed.
If Warning doesn't produce any results, checkmark Error instead.