Comment 3 for bug 82312

I believe that whenever you upgrade the kernel you need to reinstall the proprietary drivers. Can you include your xorg.conf or just see if it modified what drivers it's using?

Try referring to http://doc.gwos.org/index.php/Latest_Nvidia_Edgy

It kind of backs up theory by stating:
 "Every time you change or upgrade your kernel you will have to reinstall the Nvidia driver, no matter which method you used to install the driver."

It will also show you how to install via command line in recovery mode. It says it's for edgy but I am pretty sure it's the same method for feisty.