Invalid serial number for Photoshop CS2 - LOCKED Dead Program

I am trying to install Photoshop CS2 but it is telling me I don't have a valid serial number. I initially installed it via disc but in order to fully install it and have it after the free trial, I was told I had to uninstall it and then reinstall it via this link:

http://helpx.adobe.com/x-productkb/policy-pricing/creative-suite-2-activation-end-life.html.

However, when I try to type in my serial number, it tells me that "This is not a valid serial number. Please go back and re-enter your serial number."

I really hope that this product isn't "too old." In the link above, it states: "Adobe strongly advises against running unsupported and outdated software. The serial numbers provided as a part of the download may only be used by customers who legitimately purchased CS2 or Acrobat 7 and need to maintain their current use of these products." I did legitimately purchase CS2 and do need to maintain my current use of the product so I would appreciate it if I could continue using it.

Just to be clear I am running this program on the same Windows PC as before.

Does anybody have any ideas? They would be greatly appreciated. Thank you!