My PS3 won't sign in to the Playstation Network.

It’s happened to me many, many times before. It sorts itself out after a little while, at least in my experience.

You might want to just double check your WEP key, just in case. Make sure everything is correct in the network settings.

If you have a PSP (or any other wireless, internet capable device – a laptop, iPod Touch, etc), try to see if you can connect to the internet using that. If you get an error on that, it’s time to phone in your ISP. It might be a server-side issue.

Before you do that, you can also try to reset your router: Turn it off, disconnect the coaxial cable and wait a few minutes. Reconnect the cable, make sure the router is completely booted up (wait til all lights stop blinking) and attempt to connect to the internet using your PC that I assume you’re using now. If it’s on, check the PS3.

If that doesn’t work, I’d say give it a few hours. See if the PS3 can connect then. If not, call your ISP on Monday/Tuesday. Hope you get it sorted out; a few nights without Killzone 2 is known to drive people mad.

This happened to me a few times , turn off system switch back on .< usually sorts it .
Failing that make sure the settings are correct in the ps3 and modem/ router .