Use:
win 10 pro - Already using
latest AMD drivers 20.8.1 - Already done
windows swap file 40 gb - what is a swap file?

MSI Afteburner - I'll download tonight

PhoenixMiner 5.1c - I'll download tonight

It literally crashes straight away at the moment. I've only connected 1 power cable to max 2 gpu. Even 3 gpu crashes it - so would that suggest more software issue?

Thanks for the advice