Dell OptiPlex 755 - Manual (Page 11)

Quick Reference Guide
11
3 Connect the monitor.
Align and gently insert the monitor cable to avoid bending connector pins.
Tighten the thumbscrews on the cable connectors.
NOTE:
Some monitors have the video connector underneath the back of the
screen. See the documentation that came with your monitor for its connector
locations.
4 Connect the speakers.
5 Connect power cables to the computer, monitor, and devices and connect
the other ends of the power cables to electrical outlets.
NOTICE:
To avoid damaging a computer with a manual voltage-selection switch,
set the switch for the voltage that most closely matches the AC power available in
your location.
NOTICE:
In Japan, the voltage selection switch must be set to the 115-V position
even though the AC power available in Japan is 100 V.
6 Verify that the voltage selection switch is set correctly for your location.
Your computer has a manual voltage-selection switch. Computers with a
voltage selection switch on the back panel must be manually set to operate
at the correct operating voltage.
Set Up Your Keyboard and Mouse