How to find the serial code for harry potter and the order of the phoenix?

So I was shopping at a garage sale a few weeks ago and came across the Harry Potter and the Order of the Phoenix game. It was not in its original case, just a plain jewel case, however it looked unscratched so I bought it. When I took it home, excited to play, it asked me for the serial number. Obviously, without the main case or manual, I can't find the serial code. Is there some way to find it with just the disc?

if you have an internet connection you can download key-generator for that game...just google it and you will find it

But if you haven't internet connection just do a search in the disc for serial.txt...

It's too easy!!!