Signing in or creating an account on PS4 is virtually impossible right now, as is launching games, apps and video content on PS4, PS3 and PS Vita. You can still search, buy and redeem vouchers for games through the Playstation Store, but good luck actually downloading them, or browsing content.
Sony are well aware of the issues and are "working to restore services as soon as possible."
We are aware that users are experiencing issues logging into PSN. Thanks for your patience as we investigate. https://t.co/0H0knweLYq
— Ask PlayStation (@AskPlayStation) September 2, 2016
We'll keep you updated on the progress.