I finally succesfully installed v8.04. I followed instructions again per Jim Byram on Re-installing TMG 8. The folder for C:ProgramDataThe Master Genealogist v8 Installer was still there, so I deleted. There might have been one other remnant folder which I deleted as well. I also did a hard reboot and rechecked that all the remnant folders were still gone. I ran the install program and everything went smoothly. I had to re-enter my name/E-mail/serial number. All good.
I did not have to go into the registry. I have Windows 7.
Good luck everyone else.