My all in one pc recently went kablooey, leaving the hard drive intact. I managed to find what I thought was my serial number for Photoshop CS5, but loading it on my new machine it appears to be 4 digits too short. I don't have the email sent with the number, and it's not on adobe.com.
Is it stored anywhere in the program files that are on the old hard drive?
It not stored on you drive unless you stored it there for you use. You can retrieve you serial number from your Adobe Account at Adobe.com. Just sign in to your account using your Adobe User ID and Password find the link in My Products and Services in upper right area after signing in and click on it. A page should open and then the web server should the retrieve your registered products and display them you can click on the ones you need your serial for and it will be displayed.