To be honest, may be worth re-installing. The issue can be resolved by chroot into it from a live cd.
Since you just installed, will only take a few min. to do it again.
I never try to suggest re-installing to correct an issue....this is one example where I will.
Pay attention to the installer program when asking about grub. In most cases the defaults are fine.
How is your system setup?
Is this a dual boot with windows, or is this a single boot with linux only?
If you want to fix the install, there is a how to on the wikihttp://wiki.sabayon.org/index.php?title ... tore_Grub2
This requires you to boot a live cd and chroot into your install and repair it.
May be that another install is what you need.