Some users have success by converting the FitGirl folder into an ISO:
FitGirl repacks are famous for triggering false positives in Windows Defender and other AVs. Often, the installer tries to unpack a .exe file, the antivirus silently blocks it, and Unarc.dll throws Error 14 because it can't finish the job. unarcdll error code 14 fitgirl
This is the most critical first step. When you launch the installer, check the box that says (or 3GB depending on your system). This makes the installation more stable and prevents the unpacker from overloading your system memory. Some users have success by converting the FitGirl