Pretty much what the title says.
Later I tried a 9V adapter which I brought from home and the pedal isn't releasing any sound. On/off lights are saying it's off.
Cables and the 9V adapter from home shouldn't be the cause (tried them with another pedal and that worked).
The problem definitely lies within the pedal I lent the friend.
Also, I have no idea about electricity-related stuff. Just thought I might mention that.