Hello there,
I used to work for Argos - so bonus
The 30 day money back guarantee is not valid on games / software / ipods etc due to their nature - you could use and then take back..
Therefore the 30 day money back guarantee is only valid providing that the seal and plastic wrapping is still intact, which yours will not be as you've said..
However you are not returning the game based on the money back guarantee ... the guarantee works the same way (for example) a pair of shoes would - where if you dont wear them, you can take back... if you dont open the game, you can take back...
You are returning the game based on it not working.
You can return the game based on this principle as it is faulty.. just pop along to a store and take it back, explain the situation and ask for an exchange, and its as simple as that... the employee will then slap on a lovely yellow faulty goods sticker on it, and thats that done.
Hope this has been of help...
Just a note though - if the employee is a bit iffy about doing this, speak to the manager, or customer service manager, even the stock manager if need be... the managers will be fine about it... employees are told not to refund/exchange such products you see..