A “No Signal” screen means that there is a problem with the current input source. The TV will turn off after 10 minutes with no signal.
Turning the TV on can be done using the top button hidden on the lower left corner of the TV, or with the remote control.
The correct input can be selected with the remote control, or the bottom button on the lower left corner of the TV. Inputs are appropriately named for their purpose.
The current input is underlined. Press the input button until the desired input is the left most on the screen, and the TV will switch inputs after a few seconds.