What episode of ghost whisperer has something to do with a teenage boy who died in skateboarding accident?

The episode you're thinking of is "The Book of the Dead" from Season 1 of Ghost Whisperer.

In this episode, Melinda helps a teenage boy named Jake who died in a skateboarding accident. He's stuck in the afterlife because he regrets a prank he played on his best friend before his death, and he wants to make things right.