Is the questioner sinful when images of unveiled women appear or music is heard from the television which he helped his father set up, or is he absolved of responsibility by advising his father?

If you are not sure that your father will use the device for unlawful purposes, then there is no blame upon you for helping him. However, if he is accustomed to watching unlawful content, then it is not permissible to assist him, due to the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." If prohibited assistance has occurred, then you must repent and strive to convince your father of the necessity of using the device only for what is permissible. And one who repents from a sin is like one who committed no sin.