How to sign in playstaion network?

when i try 2 sign in PN it shows tht "U HAV BEEN SIGNED OUT OF PLAYSTATION NETWORK"....im using a wireless net and its working xcellent...the prob is its not signing in PN...it says that maintenanc e work is going on...i used 2 play before 2 - 3 months..but nw im not able to...please help me out..i desperately want 2 play online...so giv me a very gud answer friends...thx