On the main screen of game 
Hold L1+L2+R1+R2+UP-LEFT on D-Pad and Rotate left Analog stick to Down-Right.
A voice saying DEVIL MAY CRY indicate that you have unlocked everything.
But you have to Upgrade your weapons.
If this Cheat does not work mail me at Ashish-Ashu@Hotmail.com i will 
personally describe you.