You will not be able to find the license key on your old hard drive... the license key is "altered/encrypted" during install so someone who "walks by" may not find the license key
You will need to look for the license key on a sticker on the back of the disc case, or somewhere else provided with the computer
IF you registered the software with Adobe, you may go to your account at Adobe (start with the big red A at the top left) to view your information
If you go the route of booting from your original hard disk the free Belarc Advisor - Free Personal PC Audit will show you your registration key. Then uninstall and deactivate PRE. You should then be able to reinstall to your SSD and use that registration key.
Of course it may be that as an OEM version you may not be able to reinstall in which case, as mentioned above, you would need to purchase a new version.
Insanity is hereditary, you get it from your children
i'll explain how i did it so other users will get out of this annoying trouble in a fast way.
this works with HP OEM i don't know how other brands OEM works so don't ask i can't give you a correct answer about other brands.
let's start, you'll need:
hp recovery manager (if you have deleted it you can google it's download),
SWsetup folder in you HDD/SSD (if you have deleted it you can retrieve the package softwares from the recovery partition. you don't have a recovery partition? i think you made recovery disks before you deleted it if you don't well you're screwed, you'll have to order the disks from hp and they are pretty expensive).
- now open hp recovery manager (start > search > hp recovery manager)
- click on reinstall drivers and softwares (software could be applications, apps etc. i'm not sure i'm translating from the italian versione).
- select the drivers/softwares you want to reinstall
- click on install
- wait for it to finish
- reboot your pc.
and it's done you have reinstalled your OEM softwares.
hope this helps, REGARDS
First, glad that the problem was solved.
Next, thank you for taking the time to outline the steps required for recovery of HP OEM software. That WILL be helpful for others in the same situation.
As more users (and especially the "regulars" here) use the download, or physical media versions of PrE, most have no experience recovering the OEM versions. Now, we have all learned something, and have your post to link to, should another HP user come with the same problem.
Appreciated, and good luck,