my codes stop working any reason for this

[draagnfli]

first I really want to say that so far i havent had a problem getting new codes but I am curious could there be a reason that the codes i was sent to begin with would just stop working if i dont use the auto that much i only have a few but its becoming a lil tiresome to have to go back to paypal find my receipt and email it when im sure that you get enough emails with all the peep getting new pcs and all the work they do to em could there be a reason that my pc keeps dismissing the codes I am using windows XP and its a fairly new pc