This is a user forum so the serial number hasn't come from us. You need to take it up with Magix. Start with the Support link at the top of this forum.
You could also provide more details and someone here might be able to assist.
Confirm it is Movie Studio 17 that you are trying to activate
From where and how did you receive the Serial Number
What error Message do you get when it does not work?
Please note that this is a user to user Community forum and we do not send you any serial numbers. You should have received your serial number(s) for the software(s) that you bought from Magix.
Check the indicated serial number for typos. In case you purchased several applications at the same time, please check if you were using the serial number matching to the program. And check that you downloaded the right program version. E.g. Movie Studio (basic) and Platinum have their own serial numbers.