A Bootable Device Cannot Be Detected during Boot after Removing the Legacy Discrete Graphics Card

• Computer can boot normally before when using a legacy discrete graphics card.
• Error "A bootable device cannot be detected" occurring after removing the legacy discrete graphics card. Cannot boot into OS but the hard drive is detected in BIOS.
• The CSM (Compatibility Support Module) function in BIOS automatically changed to disabled and cannot be enabled manually

CSM is a feature that allows some legacy devices to boot in legacy BIOS mode on UEFI systems. This feature will be automatically enabled in BIOS when installing the legacy device on some of the platforms.

The bootloader will disappear if CSM mode is changed without re-install the Operating System.

To resolve the issue:

Re-install the Operating System with the CSM feature disabled.

or

Enable the CSM feature in BIOS. Contact the motherboard manufacturer for further support if the CSM cannot be enabled in BIOS.