the first time i install mint on 14 i did not read the patchnotes and i install a driver straight from ATI site, then i had endless issues with it, so when i found out where they moved the driver install to i went there to try and install propriety drivers and by me too it didnt show any. I had to reinstall and then the drivers showed up up in software source/additional drivers.
So maybe try reinstall, then go straight to meny/preferences/software sources/additional drivers ...
that is only thing i can think of, else keep struggling with manual drivers.
And btw, this is exactly why i made sure my new laptop doesnt have a nvidia card