When installing an after-market graphics card into a certified Windows 8 PC with UEFI enabled, the system may not boot.
When an after-market graphics card is installed into a motherboard with UEFI enabled in the system BIOS, or if the system is a certified Windows 8 PC with Secure Boot enabled, the system may not boot.
UEFI is a new system BIOS feature that is provided on most new motherboards. A UEFI system BIOS is required in order for the Windows 8 Secure Boot feature to work. Secure boot is enabled by default on certified Windows 8 PCs.
In order to get the PC to boot with a graphics card that does not contain UEFI firmware, the end-user must first disable the secure boot feature in the system's SBIOS before installing the graphics card.
Note: Some system SBIOS's incorporate a feature called compatibility boot. These systems will detect a non-UEFI-enabled firmware VBIOS and allow the user to disable secure boot and then proceed with a compatibility boot. If the system contains a system SBIOS the supports compatibility boot, the user will need to disable secure boot when asked during boot process
Instructions for manually disabling secure boot:
1) Power down the system
2) Remove the NVIDIA Add-in card
3) Boot the system using integrated graphics
4) Enter CMOS settings. CMOS settings can usually be accessed during boot, typically by pressing one of F1, F2, F8, F12, or Delete (depends on the system firmware) Alternatively they can be accessed in Windows 8 as follows: http://www.makeuseof.com/tag/how-to-access-the-bios-on-a-windows-8-computer/
5) Set Secure Boot to disabled
6) If there is an option, set CSM (or compatibility or legacy mode) to enabled.
7) Save the new settings
8) Power down the system
9) Install the NVIDIA Add-in card
10) The system should now boot
* Note that not all existing NVIDIA based cards are capable of adding UEFI support. If your card manufacturer is unable to supply you with an update, you will need to operate in compatibility mode