MEP 14 is now an old product so may not be fully compatible with your version of Windows.
Did you already own MEP 14 (and, by the way, is this MEP 14 or MEP 2014, there is a difference) or have you just bought it? If so, where from? If you previously owned it, was it installed and registered to you, so that you have a Magix account? If so, go to your account, log in, go to My products and find the listing for the product. Any activation/serial key will be shown there.
If you have recently bought the product you need to ask the seller for that key and whether he/she has previously registered the product and if so, to notify Magix (by email to infoservice@magix.net) of the sale and ask that any existing registration is transferred to you.
Please do not duplicate posts, or post your serial number or any other private information in the forum, I have hidden your duplicate comment in another post.
The serial number, P-xxxxx-xxxxx-xxxxx-xxxxx you have is the activation code, however, AFAIK these serial numbers have been deprecated and will no longer register, as this version of Movie Edit Pro, released in 2008 is obsolete.
Additionally if the computer is running Windows 10 or 11, there would be issues with running the program due to incompatibility.
Moving up to a more modern version of Movie Edit Pro - now called Movie Studio may be an option depending on the age and specification of your computer.
If you require help on this, we need to know your computer specification - see this topic for what is required and please quote processor and graphics card make/model in full, and also what monitor/screen resolution(s) your are working with.