The touch screen uses a USB to power itself, and I assume it operates on 5V
Mostly the LCD use 4.5 to 5v for driving the logic chip whereas you can also checkout the datasheet that i think one must refer to before even connecting it.(The back light current is + logic driving voltage and consumes upto 200mA's max in case of GLCD with limiting resistors)
have you checked your RX and TX connectivity are they hooked in the right way?