running a 4 wire bipolar stepper

Hello guys, I am trying to ger a bipolar 4 wire stepper motor from an old computer working with my arduino and l293D H-bridge, but the only result that I get is this:

I have tryed with different boards and different bipolar stepper, but the result is allways the same. Here is my code. Do you have any suggestions what might be wrong and where an I making misstakes. I realy need to get the stepper running. Thanks in advance

//declaration of PINS that connected the wire to motor
int nero = 13;
int marrone = 12;
int arancio = 11;
int giallo = 10;

//this is the time to wait in every single step
int delayTime = 100;

//set the pin for OUTPUT
void setup() {
pinMode(nero, OUTPUT);
pinMode(marrone, OUTPUT);
pinMode(giallo, OUTPUT);
pinMode(arancio, OUTPUT);
}

void loop() {
forward(13);
delay(500);
backward(13);
}

void forward(int steps){
for(int i=0;i<steps;i++){
// in every phase 2 wires is up and 2 is down
digitalWrite(nero, LOW);
digitalWrite(marrone, HIGH);
digitalWrite(arancio, HIGH);
digitalWrite(giallo, LOW);
delay(delayTime);

digitalWrite(nero, LOW);
digitalWrite(marrone, HIGH);
digitalWrite(arancio, LOW);
digitalWrite(giallo, HIGH);
delay(delayTime);

digitalWrite(nero, HIGH);
digitalWrite(marrone, LOW);
digitalWrite(arancio, LOW);
digitalWrite(giallo, HIGH);
delay(delayTime);

digitalWrite(nero, HIGH);
digitalWrite(marrone, LOW);
digitalWrite(arancio, HIGH);
digitalWrite(giallo, LOW);
delay(delayTime);}
}

void backward (int steps){
for(int i=0;i<steps;i++){
digitalWrite(nero, HIGH);
digitalWrite(marrone, LOW);
digitalWrite(arancio, HIGH);
digitalWrite(giallo, LOW);
delay(delayTime);

digitalWrite(nero, HIGH);
digitalWrite(marrone, LOW);
digitalWrite(arancio, LOW);
digitalWrite(giallo, HIGH);
delay(delayTime);

digitalWrite(nero, LOW);
digitalWrite(marrone, HIGH);
digitalWrite(arancio, LOW);
digitalWrite(giallo, HIGH);
delay(delayTime);

digitalWrite(nero, LOW);
digitalWrite(marrone, HIGH);
digitalWrite(arancio, HIGH);
digitalWrite(giallo, LOW);
delay(delayTime);
}

)

Obviously, you are not setting the correct pins HIGH and LOW in the correct order. Why are you not using the Stepper library?

The Thread stepper motor basics may be useful but it does not deal with L293 drivers.

If you must use an L293 follow @PaulS's advice.

...R