Computer doesn't POST after enabling Secure Boot

I wanted to enable Secure Boot to check if my PC Is compatible with Windows 11, and in order to do that, the UEFI firmware asked me to choose a Protocol/Publisher/Platform key (I don't remember exactly). I choose the default one (I think 808 pk), then disabled CSM Support, and now it doesn't boot, with the display remaining black and the keyboard LEDs flashing on and off.

• I tried everything I saw on the internet:
  • reseated CPU, RAM, and GPU
  • disconnected hard drive and connected an older one [10+ years old]
  • tried another GPU [10+ years old]
  • reset UEFI firmware with the jumper and unplugged CMOS battery overnight
    
    
• Specs:
  • MB: Gigabyte H410m s2h
  • CPU: i3-10100f
  • GPU: GTX 1650
  • RAM: 1x 8GB DDR4 2666mhz (HiperX Fury CL16)
  • PSU: Elementium Silentium E2 550w 80 Plus
  • HDD: Western Digital Blue 500GB, 7200rpm

How do I troubleshoot this?

Solution 1:

Boot the computer without any drive connected. You should be able to access the "BIOS" (or actually UEFI setup) and revert the changes you've made. Then connect the drive and boot into Windows.

Check if your drive is partitioned using the GUID Partition Table (GPT) or Master Boot Record (MBR) style. You can do this in the Disk Management console accessed by right-clicking the Start button, by right-clicking the drive (not partition) and selecting Properties.

If it's MBR, you'll have to use the mbr2gpt utility to convert it. Secure Boot requires UEFI boot mode and Windows supports UEFI boot mode only on GPT drives (at least officially). You're probably booting in BIOS mode currently, and forcing UEFI mode only with Secure Boot breaks your system.

Once you're on GPT, enabling Secure Boot should be safe - Windows's default UEFI boot setup is Secure Boot-compatible. You shouldn't have to set up UEFI keys manually though. Just turn Secure Boot on and leave everything else on defaults.