Arduino doesn't transfer data back to the computer

Hi all!

I have written a program for Arduino that reads some analog signals and sends them to the computer when it receives a command from the master computer. I wondered why this didn't work on the computer it was intended to run on. On my own computer it runs fine.

I uploaded a simple test code in the Arduino.

void setup() {
    Serial.begin(9600);
}

void loop() {
    if(Serial.available()) {
        Serial.println(Serial.read());
    }
}

This doesn't run on the second computer either. When I use Arduino serial monitor for transfering data, I see the RX led blink but not the TX. With the computer it's working on, I can see both of the leds flash. Arduino receives the data on both computers, but the second computer doesn't receive Arduino's responses.

What might be wrong?

Hmm... I forgot the Arduino hooked up to the problematic PC for a few minutes and tried it again. Now it worked! It seems like it needed some time to warm up. Why's that?

Maybe just poor USB cable connection?