If you don't wish to try an in-place upgrade repair install (see my post on the 1st page) then
a. Use disk imaging (Macrium Reflect (free) + its boot medium + external storage) to image your system...

Hi, sometimes there's no other way. We don't know all the ins and outs of the OS not being its designers.. and it's inevitable sometimes things go wrong we can't correct. I find it sad that MS...

Here are some diagnostic tools from the Tutorial section:
Storage Diagnostic Tool - Use in Windows 10 - Windows 10 Forums
...

Well, before a clean install, try this:

Using Tweaking.com's cautious repair tool appropriately (note the cautious stages), choose just repairs 1 by one that seem relevant.

If that leads to...

http://www.winhelponline.com/blog/storage-settings-drives-save-locations-windows-10/

may do it.

Good- no basic system corruption.

Try using this for the Store
App - Reset in Windows 10 - Windows 10 Forums

Ok, that shows it's a Windows issue not a profile problem.
Was this ok before you upgraded to 1607?
I have the same build.

Let's do the standard things first- worth doing anyway. Maybe someone...

Hi, have you tried creating a new user for test purposes?
What is your build level? (Windows key + R, winver)
I suspect you may be using 1511.
The ability to change this was added in a later...