I installed windows 7, and its product id is 00426-OEM-8992662-00400,I want its product key
You can still activate Windows 7.
Microsoft NEVER took down the Windows 7 activation servers 10 years ago at all.
You are the one who has to have the Product Key, not us or Microsoft.
You do not say where you got 7 from, how or what you installed it on.