Having trouble signing in to PlayStation Network?

I turned on my PlayStation for a long time and wanted to download a game. However, I can't log into my PlayStation Network account because I keep getting this error message:

I can't find anything about it on the internet. What should I do? I've turned the PlayStation on and off several times and installed the latest software update.

Enable the ports for PlayStation on your router:

TCP: 465, 983, 1935, 3478-3480, 5223, 10070-10080
UDP: 3478, 3479, 3658, 10070

And if that doesn't help either, then see whether there's a firmware update for your router and install it (you should leave the port sharing in there).