That yyy crap is almost always a speed problem for the serial communication between the arduino and the computer. Make sure that both the Serial.begin ( ) function call, and the serial monitor settting on the computer, are set to the same speed.
Add the line
Serial.begin(9600);
Serial.priintln("Hello world");
in your setup ( ) function. This will establish whether the serial communication is working, before you spa code somehow corrupts it (maybe).