I purchased the Photoshop CS about 5 years ago. My machine became dead and I no longer have the CD with me but I saved the serial number. Could I download this old version again?
I would not expect Adobe to have downloads of older versions of PS available, though could be wrong on this. If you have your S/N and you registered your copy of PS, Adobe will have a record of that - look in your Adobe ID User Account. I do not know how far back Adobe offers replacement discs for their programs, but they might be able to sell you a replacement disc for your version. To do so, they will need your Adobe User ID and your S/N, so have those handy, when contacting them.
PS always guard all installation discs, and never throw any away. I still have mine from ver. 2.5, plus every other Adobe program that I own. This goes back for decades, and is probably over 100 CD/DVD's.
IIRC, Adobe charged about US$25 for replacement discs, including shipping and handling. Only thing might be if they still sell these for much older versions.
Good luck, and please post back with your success. This comes up fairly often, but most regulars on this forum have never had to deal with it. The full details of what you hear back from Adobe could well help the next person with the same problem.
Good warning. Aside from the very, very important legal issues, there could well be a threat involved too.
With many hacked versions, even the non-threatening ones, many features will never function, if the software functions at all. Chances of getting the BBB to help you get your $ back are slim to none.