This is a user to user forum, I think you need Adobe help with a serial number
Select a topic, then click I STILL NEED HELP to start Premiere Elements Online chat
You do not have the current version of Premiere Elements (which is 13). Consequently, Adobe Chat may or may not offer support if it interprets your issue as technical rather than a straight forward sign in activation matter. But, nonetheless worthwhile for you to try for Adobe support.
But, if Adobe cannot support you on this, please report back with details of your situation
1. Premiere Elements 11 on what computer operating system?
2. Is this a "it worked before but not now" or "it never worked before issue"?
3. Where did you get the serial number....from email after purchase of the product as an online download from Adobe or from packaging of product that came in boxed packaging? Depending on the circumstances, can you verify your serial number at the Adobe web site under "My Products"?
4. Are you working with a trouble free Internet connect and with antivirus and firewalls disabled?
5. More, as the details indicate.