Hi,
After installing Windows 8.1, we may see an error on the desktop with the following message: “Secure Boot isn't configured correctly”.
This is currently a known issue for a few ASUS PC models.
Secure Boot helps increase the security of Windows 8.1 and Windows RT 8.1 PCs by stopping unauthorized software from running. If you see a "Secure Boot isn't configured correctly" message in the lower-right corner of the desktop, it means that Secure Boot has either been turned off or hasn't been set up correctly on the PC.
To turn on or set up Secure Boot, we will need to use the BIOS menu for the PC. Different PCs have different BIOS menus, so you may need to contact the PC's manufacturer for instructions.
If you have turned off Secure Boot and added own drivers then you might need to reset the PC to its original state before you can turn on Secure Boot.
Refer to:
**Returning your PC to its previous operating system**
Important: Modifying BIOS (Basic input output system)/complementary metal oxide semiconductor (CMOS) settings incorrectly can cause serious problems that may prevent your computer from booting properly. Microsoft cannot guarantee that any problems resulting from the configuring of BIOS/CMOS settings can be solved. Modifications of the settings are at your own risk.
Please let us know in case you need further help on this issue or any issue related to Windows.