Thanks for that, Slashee.
I deleted the config files in appdata. There were a bunch of old ones going back to V3.8 so I cleared them all out. I still cannot access 5.6. There is no shortcut on the desktop and nothing happens when I try the start menu.
However the version of cura that came with my recent Elegoo Neptune, which is V4.8, still runs though I just deleted the custom profiles when clearing out the config folders.
I'm on Win 10 and I want to use V5.6 as my latest project of print 3d model planes comes with custom profiles that can't be imported into V4.8 for whatever reason, hence the need for the new version. I currently have the Elegoo version installed but I have tried to get rid of all the old ones.
Steve