Hello guys...
I just wanted to know that can Crysis 3 run on my PC smoothly !!

Here's my hardware configuration:
Intel Core 2 Duo E7400 @2.80 GHz CPU
Nvidia GeForce GT 640 Graphics Card
2 GB DDR2 RAM

If not what should I do????

Well the ram is 4 GB.....sry for that..

The GPU is a bit slower than the GTS 450, that is stated as minimum system requirement. And the CPU is dual-core, that will be multiplayer performance very choppy. If you stick to single player you could try the tool by Blutaar666 for graphics lower than low: http://secure.gamesas.com/forums/viewtopic.php?f=65&t=63912

To really enjoy Crysis 3 you would need to upgrade both your CPU and your GPU.