I finally figured it out on my own. So here is what I did so anyone who has the same problem can fix it.
I investigated the theme file in username/AppData/Local/Microsoft/Windows/Theme/ that Windows was supposed to be using. In my case, it was Victorian Cosmos 2.theme. I opened it in Notepad and changed the path under visual styles from "%SystemRoot%\resources\Themes\Aero\aero.msstyles" to "%SystemRoot%\resources\Ease of Access Themes\basic.theme".
Then I went into the registry using Registry Toolkit 64bit and searched for "themes". I then found and changed the following paths:
%ResourceDir%\Themes\aero.msstyles to %ResourceDir%\ease of access themes\basic.theme
%SystemRoot%\resources\themes\aero.msstyles to...