If you still have the original CD-ROM but lost the paper sleeve with the key, you are out of luck. Unlike modern software companies (like Adobe or Microsoft) that keep a database of your purchases, Corel has no obligation to maintain a 16-year-old database of OEM keys.
The Pinnacle Studio 12 activation key was essential for several reasons:
You don’t need Pinnacle Studio 12 to render your final video. You just need the source files.
Pinnacle Studio 12 Ultimate software - VideoEditSystems.com