Player 2 : Follow player 1 and get a portal on the ground (so they’re sitting side-by-side). Now turn around 180 degrees and fire the exit portal on the right-hand slanted wall panel in front of you. Now stay by the ledge for now.
Player 1 : If you’ve positioned both portals correctly, the laser beam will pass through and hit the power receptor near you, shutting the fan off for good. If not, adjust the height/position of the portals until this is achieved.
Player 2 : Once the fan is permanently switched off, drop the Cube and then set a portal on the lower platform to your right and on the slanted wall panel behind you (directly opposite the giant fan).
Both Players : You both need to pull the switches at the same time to open the doorway, now run up the flight of stairs, locate the disc and put it into the slot to complete the second course!