Guys,
I lend my Phantom 3 Pro to someone. He swapped SD cards without powering down the Drone.

Now all there is is a blank screen with DJI Logo. Tried a few power cycles. Tried using a different SD card. Tried powering up without SD card. Same thing.

What do you think?

Hi, we're sorry to know about this situation. I would recommend resetting the camera settings and check if the firmware of your drone is updated. You may change the mobile device as well to isolate the problem. Also, would it be possible if you could clarify if you could still control the gimbal of your aircraft? If yes, have you tried to record or capture an image to see if there will be a file that would generate in the SD card? I would recommend removing the SD card, re-link the remote controller to the aircraft and check if there will be changes. Please keep us posted on the latest progress. Kindly refer to the link below. Thank you for your support.

Have you tried uninstalling the app from your device and then reinstalling it?

maybe the lens cap is still on?