Hi everyone! I just follow this guide Connecting Arduino to Processing - SparkFun Learn to learn how to communicate from Arduino to Processing and vice versa.
I just copy-paste the code into the IDEs but i received everytime the same error: COM3 busy.
I used W8.1, Arduino UNO and Processing 2.
Thank you for your advice and sorry for my bad english 
Nobody can help me? 
This may or may not help.
My wife uses a Cricut vinyl cutter on our primary desktop computer. I am unable to use my arduino on that machine unless I unplug the Cricut and restart the computer. As soon as I plug the Cricut in, I am no longer able to connect to Arduino, even if I unplug the Cricut, I must still restart the computer for it to talk to my Arduino.
Maybe this will provide some useful clues for you.
Make sure nothing else is listening for the same serial port.
Make sure the Arduino IDE is closed and try again. Also close any terminal applications.