My old laptop is dying. When I tried to install Photoshop elements 7 on my new laptop, it told me the serial number is invalid. It's the same number I used before. What gives?

I think that program is covered in the link below

CS2 (and earlier) Activation Server is gone, so read below

You MUST use the special version and serial number on the page, not your original disc or serial number

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

NOTE that CS2 will not install at all on a "modern" Mac, and when you install the special version of PPro2 on a Win7 or Win8 or Win10 computer, you MAY need to right click the program icon and select WinXP compatibility from the option popup