If You have an older nvidia graphics card you may run into problems trying to install/use Sabayon linux.

For example :

01:00.0 VGA compatible controller: NVIDIA Corporation GT218 [GeForce 210] (rev a2)

If you get an error during Sabayon live CD install, try to boot with nvidia kernel module disabled. Edit the kernel parameters at the boot menu, adding:

modprobe.blacklist=nvidia xdriver=vesa

The newest binary nvidia drivers may not support you card if it is to old. But that’s not a problem. Check what versions of nvidia drivers are avaible and uninstall the current driver:

equo remove nvidia-drivers nvidia-userspace
eix  nvidia-drivers 
# or
equo search -qv nvidia-drivers

Try installing and testing drivers in a decreasing order:

#install a selected version for your kernel: 
equo install -a nvidia-userspace nvidia-drivers-340.96#$(uname -r) 
#test
modprobe nvidia
systemctl restart lightdm

Than mask drivers above that version by adding to /etc/entropy/packages/package.mask:

>x11-drivers/nvidia-userspace-340.96
>x11-drivers/nvidia-drivers-340.96

Set OpenGL to nvidia. In some cases it helped to switch from nvidia to x11 and backwards.

eselect opengl list
eselect opengl set 2

If you get errors like Invalid parameter NVreg_DeviceFileGID … while inserting the nvidia module, just edit its parameters:

vim /etc/modprobe.d/nvidia.conf

For debugging try:

systemctl status lightdm
journalctl -u lightdm
cat /var/log/Xorg.0.log{'','.old'} | grep -E "(EE|WW)"

More:

Sabayon Wiki: HOWTO: Get AMD/ATI or Nvidia Video Cards working in Sabayon