Your MSI MPG B550 Gaming Plus Motherboard supports two versions of the Ryzen 5 5600X: https://www.msi.com/Motherboard/support/MPG-B550-GAMING-PLUS#support-main-block-qvl
Your Motherboard MUST have BIOS Version 7C56v17.zip (06/28/2021) installed for your 5600X to boot up and be recognized.
This is the latest MSI Non-BETA BIOS version for your motherboard.
Your Motherboard has the FLASH BIOS Feature where you can update the BIOS without installing a processor. Connect a USB Flash drive with the correct BIOS Version installed on the special USB BIOS port in the back of your motherboard I/O Panel.
Press the FLASH BIOS button with just power on. It should start flashing indicating that it is updating the BIOS on your motherboard.
If you have the correct BIOS Version installed already make sure the RAM MEMORY you have is compatible with the new 5600X Processor: https://www.msi.com/Motherboard/support/MPG-B550-GAMING-PLUS#support-mem-21
