Without a screen shot, it's hard to know why the footage/stills are black. Double-clicking the asset opens it in the Source monitor, as opposed to the Project monitor, which could be black if the playhead is not set to a portion of the timeline that shows a movie clip or still. Perhaps your Source monitor is closed or hidden for some reason. After double-clicking the asset, select Window > Source Monitor in the main menu. You should be able to select the specific asset (e.g., Shot_01.mp4) and then see it on the screen. Make sure you also select Window > Workspace > Editing so that your panel layout shows the various panels properly.
HTH,
Stefan