I don't know. I guess you have completed the system upgrade successfully? Maybe the nvidia drivers would affect just keyboard and mouse....I don't know. If you have completed the upgrade successfully, and still have no mouse and keyboard, you might run a few checks, such as:
eselect opengl list
(Should be a * beside the nvidia)
(That checks to see if you are missing any dependencies)
(That checks to see if you are missing any libraries)
eselect kernel list
(shows which kernel you have "set")
(shows which kernel you are booted into...the one you are currently using)
Maybe somebody else has a more definitive answer for you.
And it would be nice to know if you have completed a system upgrade successfully.