Check
this to know how to enter 'single user mode'.From there,edit your /etc/inittab file like this:
Near the top, you will see a section that looks like this:
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:
Change the line:
id:5:initdefault:
to
id:3:initdefault:
and on reboot,you can enter textmode.From there,run check /var/log/XFree.0.log for errors.Also,run xf86config or Xconfigurator/redhat-config-xfree to reconfigure X.
Also,you can install the nvidia driver from there.