Hey guys. My internet got capped when I had a few days left, so I had been playing my PS3 offline for a few days, not signing in. So not I have the internet and everytime I try to sign in it won't let me. I tested the connection and that's all fine. It's the Playstation Network that fails. HELP! 
 
EDIT: Also I had a system update (you probably all did as well) and after that I couldn't sign in.

You're doing it wrong.

Have you tried to update your system yet?  I read that there's a patch coming out today that removes the ability to run Linux on the PS3.  If you don't install that patch then you can't play online.  I'm guessing that PSN also wouldn't work.

Uh huh............

Does the PS3 browser connect to the internet?  When this happened to me I just went to the settings and disabled the connection for a second and then re-enabled it.  It said my connections were fine but I needed to reset it for whatever reason.
 
Network Settings > Internet Connection > Disable/Enable
 
Give it a shot, worked for me.

i'm also having the exact same problem.. i can't connect to PSN either but i can use the internet browser on the system and i can connect to Media Go PSN too.. WTF!

Weird, I'm not having that problem.