This has always worked for me (enable non-free repo)...
sudo apt-get install nvidia-glx nvidia-kernel-dkms nvidia-xconfig nvidia-settings
Run nvidia-xconfig as root when it's all done installing, then reboot and run nvidia-settings as root to set your resolution (second item down in the left hand menu, IIRC) and save it as xorg.conf (I don't merge w/ the old file, there's a checkbox). dkms rebuilds the module automatically when the kernel updates. Post back if there are problems.
You ran nvidia-xconfig as root and rebooted?
If still no joy, I'd uninstall those 4 packages and run autoremove, delete /etc/X11/xorg.conf and reboot, you should be running with the open source driver again. Then use smxi as suggested or install the kernel headers and try again...
$ sudo apt-get install linux-headers-$(uname -r)
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