Hi Joonie. I'm Greg, an installation specialist and 9 year Windows MVP, here to help you.
I see in your screenshot that the Yes button is missing on the UAC dialogue box. The fix for that is here: https://winaero.com/blog/fix-yes-button-disable...
You also said something about Family and Other Users being missing in Account Settings, is this correct? If so go over this checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get done: http://answers.microsoft.com/en-us/windows/wiki...
Start with Step 4 to turn off Startup freeloaders which can conflict and cause issues, then Step 7 to check for infection the most thorough way, then step 10 to check for damaged System Files. Then continue with the other steps to go over your install most thoroughly.
If nothing else helps you can run a Repair Install by installing the Media Creation Tool and choosing from it to Upgrade Now. This reinstalls Windows in about an hour while saving your files, apps and most settings, solves many problems while also bringing it up to the latest version which you need anyway and by the most stable method. http://windows.microsoft.com/en-us/windows-10/m...
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
________________________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.