Apparently Ryder spoke with an individual that he believed to be an assassin, offering the "hitman" his father’s pickup truck in exchange for murdering his parents.  The "assassin" was actually an undercover cop who’d been alerted to Ryder’s intentions by the mother of one of Ryder’s friends.  The mother had heard Ryder speaking about murdering his parents and set up the sting. 

Ryder’s murder attempt was due to his parent’s confiscation of his game consoles, his grounding, and a ban on television.