You need to pass Challenge of Olympus first.
Open up Combat Arena and set up the game as such:
Health: Unlimited.
Magic: Unlimited.
Item meter: Unlimited.
Difficulty: Titan.

Other settings will not figure into this exploit.
Enemy 1: Gorgon Serpent (set to count 3 with attack and respawn on).
Enemy 2: Gorgon (set to count 3 with attack and respawn on).

Start the match. Proceed to die five times by jumping in the air as the Gorgons 
freeze you causing Kratos to shatter (and die as a statue) as he hits the ground. 
Once you have done this, you will be asked if you want to switch to Easy Difficulty. 
Select "No" and upon choosing this, you will be taken back to the main menu.

Choose 'New Game' at whatever difficulty you like and you will now have all the 
weapons, unlimited health and a good chance to break the game by breaking things 
before you normally would(i.e Smashing the onix on the back of the Three Judges heads).