Dell OptiPlex G1 - Manual (Page 55)

Riser Board Removal (Low-Profile Chassis): Dell ™ OptiPlex ™ G1 Systems
To remove the riser board, follow these steps:
1. Remove the expansion-card cage and remove 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 that the alignment feature on the expansion-card cage engages with the alignment slot.