Case #776 can only be continued when you gain full access to the basement in the course of the main storyline missions (that is soon after the visit at the tattoo parlor and examining Helena’s memories). Initially the game only lets you investigate the area near the entrance to the basement, whereas all corridors and cellars are sealed off by closed gates.
The cellar you are looking for has the number 028 – the entrance is shown in the picture above. Interact with the panel and input the code 7441 that you have retrieved.
In the cellar 028 you can find another collectible picture, whereas the most important finding is the organ farm, as seen in the picture above. Examine it in order to learn about the available ways of concluding this case.
The first option is to reboot the device, so that the organ production process is restored. For that, focus on the two computer screens displaying the message about a critical error. Interact with the keyboards next to each of the monitors and press the green buttons in order to confirm the reboot.
The other option is to shut down life support for the organ farm and thus put it out of its misery. In order to do that interact with the lever shown in the picture and pull it down (alternatively, you can also remove the power cable plugged to the organ farm).
Regardless of your decision the case is concluded.