Dell OptiPlex Gxi - Manual (Page 73)

Riser Board Removal (Low-Profile Chassis): OptiPlex GXi
1. Remove the expansion-card cage and all expansion cards.
2. Lay the expansion-card cage on a flat work surface with the riser board facing up.
3. Remove the two riser-board mounting screws.
4. Lift the riser board away from the expansion-card cage.
When you replace the riser board, be sure the alignment feature on the expansion-card cage engages with the alignment slot on the riser board.