What computer operating system is involved?
When you first installed the program, did you go through the registration process?
You can go to the Adobe web site, http://www.adobe.com, sign in with your Adobe ID and Password, in the Search field type in My Products. Follow the My Products link to your products and look for Adobe Premiere Elements 9 in that list. When you click on Adobe Premiere Elements 9, the serial number should be revealed.
When you download replacement installation files from Adobe (from whom you purchased the product as a download specific to the computer operating system you were using), you should start with 2 files
.exe (which is either Adobe Application Manager or a Akamai counterpart
7z (which is the program itself
You need both starting with the exe which will be extracing files for the 7z.
Keys to success include
a. downloading and installing files specific to the computer operating system involved at time of purchase
b. making sure you have the set for 32 or 64 bit set of installation files.
Let us start here and then decide what next. Any questions or need clarification, please do not hesitate to ask.