Playing a used pc game?

As the other two posters have stated, if the access key has already been used, you're sort of up a creek without a paddle, so to speak. The stuff that comes in the Guild Wars box - the CD, the manuals, the flashy stickers, etc. - is completely irrelevant. The only thing that really matters is the key code, which actually determines a single account, and is sort of your unofficial "ID" on the system. If someone else has previously entered the code, you CANNOT use it. I'd suggest attempting to return the box (which is, unfortunately, all you really bought at this point), but you may find that difficult at a pawn shop. Next time, you might want to buy the game online (from Guildwars.com - they're ALWAYS having sales) or Amazon.com or something. NEVER buy a "used" copy of Guild Wars!