Hi, I just wanted to know if it is normal that my RX/TX leds (those between the two USB ports) are not bliking when I use Serial Communication?
Those two are not used for serial communications. They are connected to digital pins 72 and 73.
The other two Tx/Rx LEDs between the Power Jack and Programming port are used for serial communications on the USB Programming port via the ATmega16U2 chip.
Thanks for your answer 
But what are the tx/rx led for if they do not blink when I use the serial (not the one on usb)?