Apple iMac G5, 20-inch - Manual (Page 246)

22 - iMac G5, 20-inch Troubleshooting Diagnostic LEDs
3. Place a soft, clean towel or cloth on the desk or surface. Hold the sides of the
computer and slowly lay it down so the screen is flat against the surface and the
bottom is toward you.
4. Raise the foot and use a Phillips #1 screwdriver to loosen the three screws at the
bottom of the computer by turning them completely counterclockwise. These are
“captive screws,” which means they're not supposed to come all the way out.