QSerialPort opens Arduino but is not writting in.

Using Arduino Interfacing w/ Software on the Computer
6

Interesting, because I'm not downloading anything, I'm just open it and sending a character...That is confusing for me.

Post your Qt code. If you have a function like:

void needToSendSerialData(uint8_t someDataToSend)
{
   microPort->open();
   microPort->write(someDataToSend);
   microPort->close();
}

you will be causing the Arduino to reset every time you want to send it data.