A similar thing happened to me some years ago. Fortunately, I had registered my copy with Adobe when I purchased and first installed it, so I just called them up, they looked up my registration, gave me the correct serial number, and deactivated the copy on my old computer. They were very accommodating. As I recall, the only slightly annoying part of the interaction was waiting a half hour or so (!) on hold till one of their reps finally picked up my call.
If you did not register your purchase with them, I don't know how they will react. Since it sounds like you are talking about an older version, you might be able to sweet-talk them into helping you, especially if you sound credible (eg, not trying to install a pirated version).
Good luck,
Tom M
