if you installed it with leighs guide (see here)
you can do the following to uninstall it:
yum erase *\nvidia\*
rm -f /etc/X11/xorg.conf
But if you installed the driver from nvidia.com, then I don't know how to uninstall it. I only used ATI/AMD cards the last few years.
you can also try to use nomodeset instead of 3. It's possible that it boots into graphical mode then, with VESA drivers. But I'm not sure. After you uninstalled it, you can follow leighs guide to reinstall it.