[Moved to Premiere Elements forum.]
Did you purchase your Premiere Elements 11 Windows or Mac from Adobe?
The link that was given to you in post 1 by han-g. should contain the information that you need. Scroll down in the article to the section on "I lost my serial number or downloaded a product from Adobe". Even if you did not purchase your product from Adobe, your serial number may be there at http://www.adobe.com under My Products if your Premiere Elements 11 is registered.
We will be watching for your results.