After removing the back, you need to unscrew the power unit.

Some displays use an external "brick" and have a 12V DC power plug.

Most displays, especially larger ones, have an AC plug (wall outlet). This guide shows a display with an AC plug.

Locate the power unit and remove any screws to access it.

You may also need to remove protecting tape. This tape blocks RF noise ("static") from distorting the display. It is ok to cut the tape carefully, or you may be able to unpeel it.

Unplug all the cables that come from the power unit and supply power to the other parts of the display.

Be sure you memorize how they go back together!

It's usually a good idea to pull out your digital camera and shoot pictures of the boards before you take them apart. This will help you put them together the same way.