When I replied to your post, I was replying to an original post that came in via my e-mail today at 2:30 and was the most recent thing in the ACR forum and had remained unanswered for 1.5 hours, so I decided to reply. Had your post been put in a forum I subscribed to and happen to notice days ago, then I might have seen it, then, but didn't see it until this afternoon, and the e-mail version of your post only had the scant initial information, not the subsequent question and answer about your OS that you'd replied to on the other forum. So as you say, I had not read the thread, because it was on a forum I didn't subscribe to. So be shocked and perhaps awed as is necessary. My treat.
Second, I did make a typo when I said Win8/8/8.1 and it should have been Win7/8/8.1, which might have been deduced by the repeated 8, so you could have asked for clarification.
Seeing as you're on Windows 7 which ACR 8.4 should be compatible with, one minor detail is that I see in the compatible Lightroom 5.4 requirements that it needs Windows 7 Service Pack 1, which would mean you'd want to be caught up on your Windows Updates, which I would assume you'd be.
There are direct links to ACR 8.4(.1) on Jeff Tranberry's blog that are distinct for PS-CS6 and PS-CC so maybe that is what isn't right?
You might check what version of PS-CC you have. 14.2.1 is the most current, and maybe that is prerequisite to ACR 8.4.1, I don't know.
If worse comes to worse, uninstall everything Adobe, then run the CS Cleaner then re-install CC Desktop and see what happens as you install PS-CC and it's updates. It may need to be run several times.
Once you're ready to retry your installs, you also might try to Quit CC Desktop and run it As Administrator in case there is a permissions issue.
The CS Cleaner can be found, here:
Use the CC Cleaner Tool to solve installation problems | CC, CS3-CS6