Device shows a black screen even though I know it's powered.

Have you tried resetting the SMC, and/or PRAM? Most of the time you can fix a MacBook with these commands. If these don't work it might be a display issue, try checking if the display cable plugged into the logic board is loose. Try taking it out and plugging it back in again. You could also see if it is just a bad display by hooking it up to another monitor. If nothing displays to this, then it is a graphics chip issue. If the monitor works then you will need to replace the display assembly, if nothing displays then you can try checking the drivers. This most likely isn't the issue and it is probably something with either the logic board or the display.