What error message do you receive when you attempt this activation? Please quote the wording in full or, better still, show us a screenshot of the message.
If the problem is that you have already activated your software twice, there is a limit of two activations being possible at the same time. In order to resolve this you can go to your Magix account, log in, go to My products and find the listing for whichever version of Web Designer you have. Click on Show more details and deactivate any installation you no longer want or need. Log out, wait a few minutes and then try again to activate your new installation.
Please do not post serial numbers in the forum, or any other personal/confidential information.
This is an open, ie public, forum not Magix support.
From the image posted you have a spare activation slot available so the number of activated computers would not have been an issue.
. . . . but my installation does not work . . . .
Are you getting any error messages - if so and the message is Error code -14 this means that you're putting a valid MAGIX serial number into the wrong MAGIX product or version/edition
Did you download the installer files available in the My Products page of your account at magix.com?
If not Error -14 or no error messages, then please clarify what is not working.
Please answer the questions you were asked, rather than introducing a different question!
We are fellow-users, not Magix staff and have no means of accessing ANY detail of your account. Only you can see which is the latest version on your account.