are you using the default installed nouveau driver????
or
did you black list it and install the kmod-nvidia
or use the NVIDIA.run
the nouveau driver will not use cuda tool kit 5
you need the nvidia driver
see the fedora forum GUIDE for installing it
"F17 Nvidia guide "
http://forums.fedoraforum.org/showthread.php?t=280750
and the WARNINGS on the nvidia dev pages about too new of a version of gcc
there is a fedora 16 version
https://developer.nvidia.com/cuda-downloads
unless you are using the old toolkit 4
that one has a fedora 13 build