Adobe is the only one who can take care of that matter for you.
Click on the following link, and, when it opens, click on "Still need help? Contact us." to open Adobe Chat to discuss the topic "Serial Number Issues or Activating My Product".
Just in case notes.....Adobe allows you to put the purchased serial number on no more than 2 of your computers. Remember Deactivate is not the same as Uninstall. For Premiere Elements 10, Deactivation is done in an opened project under Help Menu/Deactivate.
Please let us know the outcome.