I have opened up my friend's laptop and cleaned up the fan and changed the thermal paste. Then, I closed it up and the screen did not work. Also, connecting a monitor via VGA doesn't help, the monitor does not show anything.
On the motherboard, near the screen connector, there is an IC with designator U1, and I am guessing it is an LDO. It is marked 1Y=61J.
Two pins, 4 and 5, are shorted together and I measure 3.4 V on them. On the other pins, I measure nothing, and they are not shorted to ground except for one pin, pin 2, which is obviously the ground pin. Pin 3 goes to a capacitor and to the screen connector. I've checked the fuse and it is shorted.
The problem was with the male connector. I have accidentally damaged some pins while connecting it. Problem is solved now. Also, it seems like this is not an LDO, instead it has some kind of transistors that pull some pins to GND.