1. Please ensure you already updated to the supported BIOS.
For motherobard A320MH please update to the BIOS "A32ESC03.BSS" or later BIOS.
BIOS Download --> https://www.biostar.com.tw/app/en/mb/introduction.php?S_ID=999#download
2. After BIOS update process completed please restart the system and turn off the AC power source.
3. Remove CMOS battery of the motherboard and clear CMOS jumper.
4. After finished clear CMOS jumper AMD Ryzen 4000 series processors can be used with A320MH motherboard.