the exact same thing happened to me, and luckily its a very easy step of installing nvidia drivers. you need to edit your XF86config-4 file in /etc/X11 (if u have Xfree86 4x), or XF86config for earlier versions.
replace the line:
In the Module section, make sure you have:
You should also remove the following lines:
if they exist.
the full of this guild is found on the nvidia site, if u need more assistance.