OP: You say you are the only user on the computer. What will most likely work, is turning off UAC (User Account Control) - in Windows 10 it's a pretty useless feature for me personally, because when I use Windows I'm fairly careful with what I download and install.
You're going to go to Control Panel > Family > User Accounts (Forgive me if it's different, I went back to 7 a couple of weeks ago and forgot exactly) and from there there should be an option to set when UAC notifies you. Turn it all the way down. UAC is still active in Windows 10, but as you yourself are the only user of your pc, if you can trust yourself, you can turn UAC off and have no issues unless you go to known bad sites or download bad files. Even then, 10 has built in protections other versions of windows do not.
After you turn UAC all the way down, restart your computer, reinstall Oblivion one last time, and everything should be fixed.
Of course, if you're not comfortable with turning off UAC (Some people are not, idk why) then you could google for more solutions, but this is the only one I know of that has a good chance of working without wasting too much of your time. It should also fix your other bethesda games.