If you need to register to use it and you can't, then that's grounds for a return isn't it?
I'm assuming it was sold as "used/working", which it isn't without a valid serial number.
Send it back, having ripped an ISO (and done a shit in the box).
Comment withdrawn because the seller turned out to be honest and very nice.
Swap it for something else at a Cex store?
If it's only a fiver, explain what's wrong with it and ask for a full refund, stating that it's not worth any more of your time and money to return it. Worked for me with a couple of dodgy low-value items.
@M_V started
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If you need to register to use it and you can't, then that's grounds for a return isn't it?
I'm assuming it was sold as "used/working", which it isn't without a valid serial number.
Send it back, having ripped an ISO (and done a shit in the box).