Are you using the daily/monthly ISO image for the installation?
From personal experience and from the posts on Sabayon's Facebook page, the newest version of the Anaconda installer is causing serious issues during the installation process. Have you tried using the 'old' 14.01 ISO image and then upgrading to the latest package versions?
Je me regarde pour me désoler,
je me compare pour me consoler
Maurice de Talleyrand