What is the religious ruling on renting out computer devices that contain impermissible music, to which people dance at mixed-gender weddings where attire is immodest?

It is forbidden to rent out equipment to someone who is known to use it for unlawful purposes, as this constitutes cooperation in sin and aggression, which is prohibited. Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." If you know that the device will be used for unlawful music, dancing, and the mixing of boys and girls, then this is clear assistance in wrongdoing. Therefore, you must avoid it, because whoever abandons something for the sake of Allah, Allah will compensate him with something better, and "let not the slowness of provision lead you to seek it through disobedience to Allah, for verily, what is with Allah cannot be attained except through obedience to Him."