Do a search around the forums, including the stickys listed on the main page, about NVidia cards. I'm not running Fedora on a machine with NVidia, so haven't been paying attention, but those might be of help.
Ah, here it is.
If none of that works
2 other possibilities.
You can, in the terminal, become root. (Use su - with the space and dash at the end)
Stuff will happen, then they'll give you instructions to test it with X -config xorg.conf.new (or something similar, I haven't done this in awhile, but they will give you the command to run to test the configuration. It might not show a mouse, but that's sometimes not a problem.
If you do get X after doing that, you can put it into your /etc/X11 directory, renaming it to xorg.conf.
The other option if that one brings you no joy
yum install system-config-display
Once it's installed, run it with the command, oddly enough, of
That will, if things go well, create a working xorg.conf file for you.