PS3 network sign in problem

after many hours of trying obvious things, ie: quitting game, test network connection, reset modem(wired ethernnet Broadband) reset PS3, adjust network configuration, everything i can think of,.... SOMETIMES it decides to work. I play Call of Duty MW2 alot and now i have not been able to sign in. My network connection test says my I.P adress-succeeded, internet connection succeeded, but Playstation Network failed. Im f#@king pissed off!
Seems to me im not the only one with this problem, so any SOUND advice would be much appreciated

Peace