The Moneris VX 520 terminal does not have an ON/OFF switch.
The VX 520 All-in-one Connection and Power Cables
IMPORTANT: You must use the exact power adaptor and cable provided with the terminal by Moneris. Failure to do so may affect the operability of, or cause damage to, the terminal.
To power up (or turn on) the terminal:
Plug
the power cable's barrel connector (1) into the power port (2) labelled
with the 
symbol located
on the Magic Box of the all-in-one connection
cable.
Plug the other end of the power cable (3) into a power source e.g. a wall jack or a power bar.
The terminal is ready when the applications menu appears.