[TippeX]

Well generally, you have no serial, your only course of action is to contact the publisher as to what to do.. Because you bought it second hand (technically) they may do not do anything, they may give you a key or sell you one at a reduced price..

If you do this, think of your story..do you tell the truth and hope for the best?, do you send a photo of the disk, box etc and say you moved house, got a new pc and discovered the manual missing? etc...the choice is yours

You could also try buying a new key on ebay or one of those cdkey sites, obviously this could be risky and you may lose more money...