There are a few issues here. Firstly, by default Mint enables Compiz...which makes navigating your way around the nvidia X Server tool virtually impossible, due to it jumping all over the place with every mouse click. If this is an issue for you, first turn off Compiz by choosing "None" under "Visual Effects" in "Appearance".
Secondly, after installing the propreitary nvidia drivers and restarting, type the following into a console.......
.....to bring up the "Screen and Graphics Preferences". Under "Screen" choose a suitable monitor type and resolution and under "Graphics Card" choose the nvidia driver and not the "Vesa" driver. "Test" if you like and then hit "OK" if all goes well.