How to connect rasberry pi 400 (keyboard) with an element 14 7" Touchscreen display.

Question

How to connect rasberry pi 400 (keyboard) with an element 14 7" Touchscreen display. 
 I tried to connect the 7" Touchscreen display the same way i connect the keyboard with a normal monitor but the screen does not turn on. 
 i have seen other tutorial where people normally connect the screen with a normal pi 4 and then the keyboard but, i think there should be better way to connect the 7" touchscreen with the pi keyboard directly.

ralphjy · Answer

It would be useful if you provide the part number of the display that you are using and describe how you have it connected. 
 I assume that you are using an HDMI touchscreen similar to the DFRobot DFR0506 https://www.newark.com/dfrobot/dfr0506/7-hdmi-display-w-capacitive-touchscreen/dp/87AH5890?st=hdmi%20touchscreen . That display requires a USB connection for power and touchscreen data in addition to the HDMI connection.