I'm assuming Windows 10
You just need to input a generic product key since the serial is embedded on the mobo
depending on the version
Home: YTMG3-N6DKC-DKB77-7M9GH-8HVX7
Home SL (most likely this is what you need): BT79Q-G7N6G-PGBYW-4YWX6-6F4BT
Pro: VK7JG-NPHTM-C97JM-9MPGT-3V66T
These are generic Windows 10 serial -- and these are legal *if* you have embedded serial on mobo -- if you don't have an embedded serial on the mobo, it will not work