The PlayStation Network is experiencing login and account managment issues at the moment, and have been for some time now. Sony is aware of the problem, issuing this statement:
PSN services are beginning to restore. However account management functions are still unavailable as we continue to reinstate full service.
The issues are affecting both the PlayStation 3, with a Error 8071-53D message, and the PlayStation Vita, with a NP-2239-6 message.
Similar problems surfaced last weekend, but was swiftly handled by Sony's PSN team. At the moment, it doesn't appear to be related to any hacking, but we'll keep you posted should any other information arise.