Take the exit from the room on the metal balcony, then crouch and squeeze through the small hole in the wall located directly under one of the light sources.
Soon you will reach the room with three red levers. Ignore them, because you cannot restore power supply at the moment. Instead, take a look at the large machine that currently has only one cable attached to it. The other two cables lie on the ground. You have to pick each one up and put in one of the free sockets.
Take note of the six small switches located on the left. Start interacting with them and determine that the fifth fuse is fried. Locate it and press the interact button in order to remove it.
Explore the surrounding corridors, which will take you to the fuse box shown in picture 1. Pull out the right upper fuse (10A). Return it to the board with six small fuses. Place the new fuse in the fifth slot and press the switch. All lights should now turn green (as shown in picture 2).
You can now return to the central console with the three red levers. Move the left lever down so that it turns green, BUT do not move the other two levers right afterwards. Wait with the second lever, until it starts flashing on the computer screen - this will happen right after the white bar is filled up (see the picture above). Approach the final lever identically and pull it after the progress bar is about 2/3 of the way towards being full and when the icon of the third lever will start blinking on the screen.