Without knowing what exactly failed (Elgg version, error that occured) it's impossible to give any advice.

Softaculous is responsible for getting any auto-installation of software to work. Maybe it doesn't work with recent versions of Elgg at all. Or maybe Softaculous can't resolve the requirements of Elgg correctly. Anyway, the manuall installation of Elgg should work in any case as explained at http://learn.elgg.org/en/stable/intro/install.html. Maybe the requirements (e.g. php 5.6 at minimum) where not fullfiled on the server. If you would provide more info about what error has occured in your manual installation attempt we might be able to guide you through the installation process.