Over Christmas Eve and Christmas Day, PlayStation Network and Xbox Live were both attacked by a group that call themselves the "Lizard Squad". This group has been harassing Microsoft and Sony by bringing down online service since early December or even earlier then that. They were even responsible for diverting one of Sony's executives flights on a plane with a bomb threat back in August. This is the reason why you haven't been able to get online.
If you want to see an interview with the Lizard Squad, Click here.
If you want to see an interview with the Lizard Squad, Click here.