If the output is displayed in an LCD, why do you need the serial monitor?
Which Arduino are you using?I have achieved what you want. If you don't want to plug your prototype to a PC you have to use an external supply for powering the Arduino.
You just need an input (Keyboard and usb shield), an output (LCD) , an external supply (AC/DC adapter 9V) and the Arduino.
I see, the Arduino just fooled me.haha BUT it's inconsistent because most of the time the key is not sent and displayed in the LCD and testing it I think it is not initializing during the time I run "Usb.Task()" and get inputs from the USB keyboard.