Black screen with cursor after successful Windows 10 upgrade
Solution 1:
I found the answer. It was because I had installed OldNewExplorer before to modify which folders display in "My Computer" and I think it was to bring back libraries in Win 8.1.
People have reported problems when explorer has been modified by things such as ClassicShell etc. Anything that modifies explorer may break the Win10 upgrade.
I uninstalled OldNewExplorer and the upgrade completed successfully.