Where can I find the serial number for my Adobe Photoshop Elements 11 program?

I purchased Adobe Photoshop Elements 11 a couple of years ago and had it installed on my old laptop, and now I am trying to install it on my desktop computer.  I cannot find the serial code anywhere on the box or DVD envelope, and I have tried entering every code on the box I could find (all invalid).  It's supposed to be a 24 digit code with letters and numbers, right?  I looked at my account to see if I had any products previously installed, but it says I don't for some reason.  I also tried checking my email to see if I had been sent the code, but I wasn't able to find anything.  I obviously had the code at some point since I was able to install the program a few years ago, so I'm not sure what happened?  Can anyone help me?