How do I get the 26-character code for my OS

I have an old 286 or 386 computer that became infected with a trojan so I haven’t used that computer for about 5 years. Recently, I found the recovery disc that came with the computer and there was a label on the envelope that I thought had the the ownership code but, when I tried to use the disc, it asked for a longer (26 character) code to allow me to use the disc for reformatting. I can only assume that it is asking for the original authorization code for the OS itself and I no longer have a record of that. Does that 26-character authorization code exist in my old computer memory?