COM# Port missing, Attempt to communicate between MATLAB and Arduino.

Development Tools IDE 1.x
1

My COM port disappeared after I attempted to establish a serial connection between MATLAB and Arduino. It appears that the drivers no longer work. I tried uninstalling the drivers and arduino and reinstalling the drivers and COM3 won't reappear. I've now only got access to COM1 and COM2. Any ideas?

The code I ran is a simple serial test as follows:

 /*
  Communications Matlab <--> Arduino
  Arduino file 1 for use with Matlab file 1 
  L. Toms
  establishContact() routine by:
  by Tom Igoe and Scott Fitzgerald
  http://www.arduino.cc/en/Tutorial/SerialCallResponse
  other ideas from
  robot grrrl
  http://robotgrrl.com/blog/2010/01/15/arduino-to-matlab-read-in-sensor-data/
  */
   int ledPin=A6;
   int i = 0;
   
void setup() {
   pinMode(ledPin, OUTPUT);
   // start serial port at 9600 bps:
   Serial.begin(9600);
   digitalWrite(ledPin,HIGH);
   establishContact();  // send a byte to establish contact until receiver responds
   digitalWrite(ledPin,LOW);
 }

 void loop() {
 Serial.println(i);
 i=i+1;  
 }

 void establishContact() {
     while (Serial.available() <= 0) {
       Serial.println('A', BYTE);   // send a capital A
       delay(300);
     }
 }