nVidia card? Hmmm. At first, you should remove catalyst-utils and any catalyst packages, if there are others.
Chroot from live media is viable, but i think you can simply get a terminal by pressing ctrl + alt + F6 when you gets the black screen.
When was the last time since you did a full system upgrade? I think it was quite a while. So i woud do this steps:
*to remove any catalyst related stuff:
sudo pacman -Rdd catalyst catalyst-libgl catalyst-utils lib32-catalyst-libgl lib32-catalyst-utils
sudo pacman -Syu
*to get back nvidia:
sudo pacman -Rdd mesa-libgl
sudo pacman -R xf86-video-nouveau
sudo pacman -S nvidia
sudo pacman -S nvidia-utils
And also, there are some other help here: switch from nvidia to mesa