Problem connecting the Arduino Robot

Yesterday I got my new Arduino Robot Tested for few minutes (Motor test, follow line) and worked fine. While I was loading Bot_Disco, I lost the serial connection. Since then, I am unable to connect the Robot to my pc. The Robot cant be found. When I put the robot on or press the reset, nothing happens. The LCD backlight is on and thats it. The usual greeting message not displayed any more. No led blinking when press reset. I wonder if I lost the bootloader? Cable is fine. It works with the Robot motor board. Run on a PC windows 7. Tried on a mac, same problem

Please help