Every time you upgrade the kernel, you will need to reinstall the nvidia drivers. I find it best to keep a copy of the /usr/X11/XF86Config file once you have your display working properly.
Boot your machine up using the new kernel and allow it to run through to a login, then login as root.
Change directory to wherever your nvidia driver script is kept and run the script.
Don't allow it to download modules from the internet, as you want it to recompile the modules currently on your system.
Once the nvidia script has finished, your system should be working again and the old login should fail.
You can delete the old boot from the /etc/grub.conf file at this point.
This happens every time you upgrade the kernel, so that's why I keep a copy of the /usr/X11/XF86Config once I've got it working.