Windows stuck loading when i change my bios from CSM to UEFI.

Troubleshooting Windows Boot Issues After Switching BIOS from CSM to UEFI

If you’re encountering a Windows startup hang or black screen after switching your BIOS settings from Compatibility Support Module (CSM) to UEFI mode, you’re not alone. This common scenario can arise due to various configuration issues, especially when modifying boot modes and drive partition styles. Here’s a comprehensive guide to understanding and resolving the problem.

Understanding the Context

Many users need to switch from CSM/Legacy boot mode to UEFI to enable features like Secure Boot, which are often required for compatibility with modern games or security enhancements. This process typically involves:

Converting drives from MBR (Master Boot Record) to GPT (GUID Partition Table).
Changing BIOS settings from CSM to UEFI mode.
Reconfiguring Windows to boot in UEFI mode, often through rebuilding the Boot Configuration Data (BCD).

Common Challenges

Switching BIOS modes can sometimes cause Windows to become unbootable or stuck during startup, often related to:

Incomplete or improper drive partition conversion.
Misconfigured UEFI firmware settings.
Incorrect BCD store setup.
Secure Boot conflicts or additional BIOS settings interfering.

Step-by-Step Troubleshooting and Solutions

Verify Drive Partition Style

Ensure your system drive is GPT-partitioned, as UEFI requires GPT. You can confirm this by:

Opening Command Prompt as Administrator.
Running: diskpart → then list disk.
Checking if the disk shows an asterisk (*) under the GPT column. If not, convert your drive to GPT (note: this involves data loss—backup first).
Confirm UEFI Boot Mode and Secure Boot Settings

In your BIOS:

Double-check that CSM (Compatibility Support Module) is disabled.
Secure Boot is enabled.
Boot mode is set to UEFI only, not Legacy or Legacy+UEFI.
Rebuild the Boot Configuration Data (BCD)

You’ve already attempted rebuilding the BCD with:

bcdboot C:\Windows /s S: /f UEFI

Ensure that:

The EFI System Partition (ESP) (drive letter S:) is correctly formatted as FAT32 and is mounted as an EFI partition.
The command completes without errors.
Verify EFI Partition
Use Diskpart (diskpart) → list disk → select disk X → list partition.
Confirm the EFI partition exists (usually around 100-