Problem with romeo example

hello guys..im new to this world especially arduino :) i just bought 4WD and roboduino romeo.The problem is after uploading the example,it does not move.Here i attach the example i use and my 4WD romeo picture

//Standard PWM DC control
int E1 = 5; //M1 Speed Control
int E2 = 6; //M2 Speed Control
int M1 = 4; //M1 Direction Control
int M2 = 7; //M1 Direction Control


///For previous Romeo, please use these pins.
//int E1 = 6; //M1 Speed Control
//int E2 = 9; //M2 Speed Control
//int M1 = 7; //M1 Direction Control
//int M2 = 8; //M1 Direction Control
void stop(void) //Stop
{
digitalWrite(E1,LOW);
digitalWrite(E2,LOW);
}
void advance(char a,char b) //Move forward
{
analogWrite (E1,a); //PWM Speed Control
digitalWrite(M1,HIGH);
analogWrite (E2,b);
digitalWrite(M2,HIGH);
}
void back_off (char a,char b) //Move backward
{
analogWrite (E1,a);
digitalWrite(M1,LOW);
analogWrite (E2,b);
digitalWrite(M2,LOW);
}
void turn_L (char a,char b) //Turn Left
{
analogWrite (E1,a);
digitalWrite(M1,LOW);
analogWrite (E2,b);
digitalWrite(M2,HIGH);
}
void turn_R (char a,char b) //Turn Right
{
analogWrite (E1,a);
digitalWrite(M1,HIGH);
analogWrite (E2,b);
digitalWrite(M2,LOW);
}
void setup(void)
{
int i;
for(i=6;i<=9;i++)
pinMode(i, OUTPUT);
Serial.begin(19200); //Set Baud Rate
}
void loop(void)
{
char val = Serial.read();
if(val!=-1)
{
switch(val)
{
case 'w'://Move Forward
advance (100,100); //PWM Speed Control
break;
case 's'://Move Backward
back_off (100,100);
break;
case 'a'://Turn Left
turn_L (100,100);
break;
case 'd'://Turn Right
turn_R (100,100);
break;
}
delay(40);
}
else stop();
}

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