Safety Guidelines 1
Disconnect the equipment from the mains supply. Inside a PC the voltages should be safe - the most dangerous mains voltages are inside the power supply unit (PSU) - but it is still advisable to remove the mains supply power completely. Note that the voltages in monitors are extremely high, even with the mains supply removed, and only skilled and trained technicians should remove the cover of a monitor.
The same electrical safety procedure should be followed when dealing with laptops and other portable computing devices.
Note: the LCD monitor used on laptops does not pose the small threat as a normal PCs monitor. However, when working with any electrical equipment the appropriate safety measures should be followed.