The issue here is that ASUS motherboards implement Microsoft Secure Boot by default, but older operating systems like Windows 7 don't support this. After installing the KB3133977 update, the system detects inconsistent OS loader keys, which results in boot failure. ASUS provides a FAQ over here.
After you install update 3133977 on a Windows 7 x64-based system that includes an Asus-based main board, the system does not start, and it generates a Secure Boot error on the Asus BIOS screen. This problem occurs because Asus allowed the main board to enable the Secure Boot process even though Windows 7 does not support this feature.Full details at InfoWorld.
To resolve this problem, go to the following Asus support website to learn how to disable Secure Boot for Windows 7:
Note The Secure Boot feature is supported in Windows 10. To learn more about the security advantages of this feature and about the upgrade path from Windows 7 to Windows 10, go to the following Windows website: