If the EVF/LCD are black and the camera records fully dark frames even though the shutter, aperture, and focus still seem to work, the most likely issue is that the image sensor path is failing rather than the lens or exposure controls.

Based on the reported repair outcome, the fault was in the camera’s main PWB (main circuit board), which had to be replaced. So this points to an internal electronic failure, not a settings problem.

Practical next steps:

• Try a basic reset and check battery/card contacts, but this is unlikely to fix it.
• If the camera is under warranty, contact Fujifilm service.
• Otherwise, get a repair quote from an authorized camera repair shop and compare it with the camera’s used value.

In short: black live view plus black image files on an otherwise functioning X100S strongly suggests a sensor/main-board electronic fault that needs professional service.