Moved 1 stick into slot B1 and it booted so I went into BIOS.
Tried to flash latest BIOS from USB but board said it was incorrect BIOS. So, tried direct from internet instead - again, incorrect BIOS apparently!
So, switched off and went on another PC to download ALL BIOS files from Asus website for the board! Back to the Ryzen...... red LEDs again, won't boot!