As far as I understand you are now in the situation that you cannot even install it. This points to other issue with the system. Do you have full access to the system? Any hard disk or permission problems? Have you tried before trying to install to run the ZA removal tool again always followed by a reboot.
Is your user profile corrupted?
Have you tried to create a new user in the system and install from there?
I am quickly running out of ideas, Sorry.
I would also seriously think to upgrade to a supported OS.