Windows somehow downgraded from 8.1 to 8 Build 9200?

[Hunter-AP]

Last night I had installed "Update for Microsoft Sharepoint Server 2013 Client Components SDK (KB2817619) 64-Bit Edition", and suddenly this morning Windows downgraded to Windows 8 Build 9200. I noticed everything that I installed when I originally got the Windows 8.1 update or required Windows 8.1 is now buggy, and the bottom left-hand corner above the desktop clock says "Windows 8 Build 9200". If I try to revert my system back to a previous restore point, the earliest in yesterday, but after I installed some large programs and moved/deleted a large number of files around on my computer. If I try to reinstall Windows 8.1, it doesn't show up on the Windows App Store despite any solutions the Microsoft website recommends.

Does anyone have any ideas as to what I can do to fix this issue? It's extremely annoying to deal with and I'd rather find out about a quick-fix than to call up Microsoft and deal with customer support (Long story short, I've had some bad experiences with them). Any and all help is appreciated, guys.

[gooooooooooogle]

are you sure it downgraded? are the 8.1 features still there?

[Hunter-AP]

Windows 8.1 features for the Start Menu are all still there, but everything relating to desktop updates aren't working properly.
EDIT: Also, when checking in the Control Panel what version of Windows I have, it says I have Windows 8, when it used to say 8.1

[birkett]

That's a completely knackered install then. At this point, there's little chance of a once shot fix, SFC will sort out the system files, but will leave SxS in a mess. The registry will most likely be a mess to - so a reinstall is the best fix.

If you can get hold of an 8.1 ISO, your original 8 key will work, and save you the hassle of upgrading from the Store.