The only thing you can do is find it again.
If you purchased the game from VSTEP then you can prove that you have bought it and they can help you out.
If you have proof of purchase from another place that you have bought it at, then you can also provide this proof and you can be helped out.
but without either of these things, I am afraid you cannot be offered assistance. And quite frankly, if there is some other reason for your problem, like your license key coming up as "invalid" during install or after patching the game, we would vey much appreciate honesty.
Regards,
Fred
