Are you sure that your Premiere Elements 11 is not registered? To be extra sure, go to
http://www.adobe.com, sign in with your Adobe ID and password, and click on My Adobe at the top of the page. Then look for the header My Products, then the name of your product, and hopefully the serial number will be there.
Some of these registrations were automatic with the Sign In with the Adobe ID and password.
Please let us know if that worked for you.
I checked, and the only product I have registered is Photoshop CS2, not Premiere Elements 11
The only hope that I see is you finding the serial number among what you have. Please assure that you are looking in the correct place for the serial number.
I purchased Photoshop Elements 11 and Premiere Elements 11 bundled in box packaging. There was a smaller box inside the outter box. A white box with an Adobe emblem slide out from the latter smaller box. On the back of that while box with the Adobe emblem were labels, one with serial number for Photoshop Elements 11 and one with serial number for Premiere Elements.
Inside this white box with the Adobe emblem were two envelopes, one for Photoshop Elements 11 Premiere Elements Windows and one for Photoshop Elements 11 and Premiere Elements 11 Mac.
Do you find any or all of the above in what you stored after you installed your Premiere Elements 11 Windows?
If not, I know of no one who can help you in this matter.