L297 + L298 circuit not working

#define stepPin 4
    #define dirPin 5

     void setup() {
     Serial.begin(9600);
        Serial.println("Starting stepper exerciser.");

         pinMode(stepPin, OUTPUT);
          pinMode(dirPin, OUTPUT);

            digitalWrite(dirPin, HIGH);
                    digitalWrite(stepPin, LOW);
                          }

               void loop() {
               int i, j;

                      for (i=1000; i>=200; i-=100) {
Serial.print("Speed: ");
Serial.println(i);

for (j=0; j<2000; j++) {
  digitalWrite(stepPin, HIGH);
  delayMicroseconds(i);
  digitalWrite(stepPin, LOW);
  delayMicroseconds(i);
}

delay(500);
digitalWrite(dirPin, !digitalRead(dirPin));

for (j=0; j<2000; j++) {
  digitalWrite(stepPin, HIGH);
  delayMicroseconds(i);
  digitalWrite(stepPin, LOW);
  delayMicroseconds(i);
}

delay(1000);
Serial.println("Switching directions."); 
digitalWrite(dirPin, !digitalRead(dirPin));
       }
         }