sounds like you've installed the nvidia driver, and simply need to reinstall it, after each kernel update-
if so-
boot to init 3
cd /to/where/ever/the/driver/is/located
(you can download it from nvidia.com)
sh NVIDIAwhateverversionyouhave.run
finish all the prompts from the driver
sax2 -m 0=nvidia
finish up the prompts from sax2
FYI- you'll need kernel sources for the driver from NVIDIA.com
hope it helps!