We claim the ornamental design for a display panel of a programmed computer system with a graphical user interface, as shown and described.
The FIGURE is a front view of a display panel of a programmed computer system with a graphical user interface.
The broken line showing of a portion of a display panel is for the purpose of illustrating environmental structure and forms no part of the claimed design. The broken lines showing of portions of the graphical user interface within the display panel form no part of the claimed design.