Serial port connection with Arduino Uno

I am using Windows8 and was just trying to set up serial connection to the server. i firstly uploaded the sample sketch and then run the instructions in the sketch code. But there is a problem that i cannot solve. This is what happened in the CMD.

Does anyone know how to fix it? COM3 is indeed the port I am actually usinng!

Hola saludos a todos compañeros,respecto al tema del puerto serie tienes que tener conectado el arduino al usb y al puerto com respectivo osea el com 3 y tienes que tener el ide de arduino activo o si no no conecta verifica que ese puerto no lo este usando otro dispositivo…

In your cmd window type in the command “mode” and report back the results.

My other suggestion is to make sure the serial port is not already in use by something else, maybe serial monitor in Arduino IDE for example.