See if it will work if you boot your computer into safe mode.
Hold the shift key while clicking restart. When you arrive at the appropriate screen select #5 safe mode with networking.
IF not....
Enable the hidden administrator's account and see if it will work in that profile.
Admin command prompt type
net user administrator /active:yes
hit enter
type exit
reboot and log on as administrator
IF not....
Try a combination of the two ..... safe mode and hidden administrator account.
Failing all, it might be time for an in-place, upgrade repair installation
There is a pretty good article here
https://neosmart.net/wiki/windows-10-repair-installation/ just ignore the first couple paragraphs where they are promoting their repair products and scroll down to the meat of the article.
If you do not have the installation media....
The installation media can be obtain through either of these two resources.
https://www.microsoft.com/en-us/software-download/techbench
OR
http://www.microsoft.com/en-us/software-download/windows10
Once you have the ISO, you can use ImgBurn to burn it to a DVD or Rufus to burn it to a USB ThumbDrive, or simply mount the ISO from within Windows 10 and run setup.exe from there.
Choose upgrade and make sure the box is ticked to obtain updates as part of the upgrade process.
This is a relatively simple and straight forward task and is generally non-destructive (all your data, programs, drivers, etc., should remain intact and unharmed), but.....
Personally I would still have a backup of my critical data, as well as a disk image, so I could recover in the event of some unforeseen problem.