My friend as much as i would like to tell you to search for topics like this already started im not an administrator or moderator neither i want it to be, but
do this...Type in Terminal:

sudo -s (after that put your password) you'll notice it will appear in root mode like this "bash-3.2#"
cd /system/library/extensions/ && chown -R root:wheel * && chmod -R 755 *
diskutil repairpermissions /
reboot

Tell me if that make a difference (supposing you have the correct NVinject and the Nvidia Installer already)
hope it helps