Hi Alessandro,
It would be useful if you can provide some more detail on your set up. Where/when did you get your board, is this the CPU only board or the complete TWR kit with elevators and the TWR-SER or TWR-SER2 and TWR_RGB display board?
What revision of CPU card do you have, assumption would be this is rev G, look for the label on the bottom of the board SCH-27442 REV _ ?
If you have the full kit with RGB display module have you been able to assemble the kit and run the OOBE with the supplied micro SD card, do you see a flash screen and then the demo come to life with touchscreen inteface etc?
In theory you should have to do nothing with a new kit except assemble, insert SD card and power on, are you using a dual headed USB cable with both heads plugged in?
What environment are you using, native Linux machine or virtual environment set up, if virtual have you connected your serial interface to your virtual machine, what settings have you used for you serial port, how did you determine the serial port to use etc, can you try using a Window's terminal to eliminate some of these possibilities?
There are a lot more questions I could ask, but please try to provide a more detailed description of your set up first, this will help.
Thanks
Ross