This is a user to user forum to help learn the product, not Adobe support... you need Adobe support
Select a reason, then click I STILL NEED HELP to activate Premiere Elements chat
As John T. Smith has pointed out, Adobe via its Adobe Chat is the only one to resolve serial number/activation matters. We are not Adobe, rather a user to user forum.
But, I would ask "In what way does not Premiere Elements 11 not recognize your serial number?
a. when you insert the purchased serial number as requested, you get an invalid serial number message?
b. your serial number is accepted (no invalid serial number messages), but you cannot open a new project?
If it is "a", then perhaps Adobe Chat "Activation" will resolve the problem, if not, it will either reject the report or transfer you to another Chat group.
Please let us know the outcome.