Question The classic ' "No Bootlable Devices Found" error ?

[no_boot_found]

I've played around with what have been at least a couple dozen different setting arrangements last night, and to no avail as of yet. I'm not an expert at this stuff; I tend to only address BIOS and related settings when an issue like this pops up.

The SAMSUNG SSD is the primary boot, with the ADATA acting as additional storage space.

Here are the specs:

These are pictures of the most recent settings I have it at:

 

[USAFRet]

A little backstory on this, please.

All the parts involved?
What was the last thing you did before it started doing this?

 

[Misgar]

Although you've got the Samsung 870 EVO at the top of the list, there might be another BIOS entry where you can select "Windows Boot Manager", in addition to specifying the first bootable SSD. If I get this wrong on my Asus boards, they may not boot.

Did you touch the 'CSM Support' or 'Storage Boot Option Control' settings?

From the B550M DS3H AC manual:

CSM Support
Enables or disables UEFI CSM (Compatibility Support Module) to support a legacy PC boot process.
Disabled Disables UEFI CSM and supports UEFI BIOS boot process only.
Enabled Enables UEFI CSM. (Default)

Storage Boot Option Control
Allows you to select whether to enable the UEFI or legacy option ROM for the storage device controller.
Disabled Disables option ROM.
UEFI Only Enables UEFI option ROM only. (Default)
Legacy Only Enables legacy option ROM only.
This item is configurable only when CSM Support is set to Enabled.

Also check SATA configuration is not set to RAID. Normally it's AHCI.

SATA Configuration
& SATA Mode
Enables or disables RAID for the SATA controllers integrated in the Chipset or configures the SATA controllers
to AHCI mode.
RAID Enables RAID for the SATA controller.
AHCI Configures the SATA controllers to AHCI mode. Advanced Host Controller Interface
(AHCI) is an interface specification that allows the storage driver to enable advanced
Serial ATA features such as Native Command Queuing and hot plug. (Default)

If the system is attempting to boot from the ADATA drive, you could disconnect it temporarily to give the BIOS less choice of bootable devices.

If you have any USB drives or memory sticks attached, remove them. If 'boot from USB' is higher priority than 'boot from internal SSD/HDD', the system may hang with OS not found.