if I am understanding you correctly.
you had the live DVD up running and working.
using the shortcut on the desktop you double clicked on the shortcut, updated the installer, quit and it reloaded the installer you ran through it and then installed and it stalled at 70% ?
then you changed desktop environments while it was still installing/stalled at 70% ?
just trying to find out what you did so people can understand the events that happened so we can give advice.
also try to include some info about what kind of computer and hardware you have(nvidia, ATI, intel)
check out the new user resourceshttp://forum.sabayon.org/viewtopic.php?f=86&t=16505
bookmark this and read it while you are waiting for more people to answer this.