In that case, I strongly believe, that there is something like a gaming mouse-driver, modem-software or something other running, which blocks the serial data-flow.
Try to run that script in this way:
int led = 13;
#define MySerial SerialUSB
// the setup routine runs once when you press reset:
void setup() {
// initialize the digital pin as an output.
pinMode(led, OUTPUT);
MySerial.begin(19200);
}
// the loop routine runs over and over again forever:
void loop() {
digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level)
MySerial.println("HIGH ####");
delay(1000); // wait for a second
digitalWrite(led, LOW); // turn the LED off by making the voltage LOW
MySerial.println("LOW");
delay(1000); // wait for a second
}
and if that is not blinking, run the DigiX from external power and without USB connection.