in your /etc/X11/xorg.conf you should be having a section 'Device' with 'Driver' set to 'nvidia', assuming that you have installed the nvidia drivers from the net, not the default shipped driver from Fedora.
if you change that from 'nvidia' to 'nv', my experience is that you are using the stock Fedora drivers again enabling your box to work again.
My assumption is based on the fact that with a new kernel, you are missing the custom built nvidia modules for that particular kernel.
If you happen to have boot problems due to this, edit the boot command line in GRUB (again, assuming you are using GRUB), removing the 'rhgb' part, and adding a three ('3') to it, it boots text-only to runlevel 3, so you can alter the config file.
you can test that X is working again with 'startx' just before going into runlevel 5 again.
Hope this helps.