[SOLVED] Can't boot from SSD on Asus Prime z390-P

Sep 14, 2019
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Parts
  • Motherboard: Asus Prime z390-P
  • CPU: i7 9700
  • RAM: 2x8Gb Corsair Vengeance 3000MHz
  • SSD: Samsung Evo 860 500Gb
Problem
I installed Windows 10 64 bit from UEFI usb, onto my SSD, but after the installation, the SSD doesn't show up as a bootable device. It however does show up as a storage device.
What I've tried
I made sure that my SSD is clean, and it has a GPT partition on it (cleaned it completely and converted it to GPT). I have re-installed Windows with both CSM disabled and enabled, also tried disabling secure boot, but the problem persists. I have no other sata devices plugged into the motherboard, and I have tested all of the sata ports with 2 different sata cables, and the satas are set to AHCI.
The only way to get my SSD to show up as a boot device, is to change CSM on and change the boots to legacy, but then I Windows doesn't boot, since it's installed on a GPT partition, instead of MRB. Windows also doesn't let me install itself, if I change the partition to MRB on my SSD.