Code:
function LevelChanger_event()
{
  if(event_type == event_entity || event_type == event_impact)
  {
    if(you == player)
    {
      my.enable_entity = null;
      my.enable_impact = null;
      level_load("level2.wmb");
    }
  }
}

This makes sure that events are only turned off if the player hits the entity.
Hope this works.