OS Upgrade has failed

I tried to run an upgrade from RHEL 7 to RHEL 8 (hardware is a tower PC with 4 RAID drives, a 2070 GPU and i7 processor). I followed the instructions here: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/upgrading_to_rhel_8/index but the post-leapp reboot led to some odd warnings around wifi and after a system restart I get warnings such as 'failed to find logical memory', 'couldn't get size' before the initial setp-up screen appears. When I then click finish configuration the screen goes black, no other tty are available. I get an occasional flicker from the screen, but nothing else. I have tried removing the graphical interface option and quiet options to see if that helps, but it doesn't. The only non-standard profile element pre-upgrade was nouveau was blacklisted and nvidia drivers were running. Any help would be gratefully received, as I tried to re-install a clean OS from a boot .iso (which I know RH don't really like, but any port in a storm) and I just get dracut-initqueue timeouts.