So you already created an account ? (e-mail and password)
When you turn on your ps3, you pick which user you want (on the left of xmb) then go to sign in.
Im trying to figure out what your exact problem is. Trouble navigating the xmb or trouble signing in?
What your saying makes me think you made a seperate user (on the left of xmb) and you havent yet signed up with PSN, so its saying "sign up for playstation network." (or has someone deleted the user you made; and signed up with)
Please post back with more info!! Welcome to the forums xXTurkeyJerkeyXx!