Because you change the SSD, so you have new pc and lose the Windows 10 license. If you use Windows 10 retail key, you can reactivate Windows 10 after a hardware change: [URL] If you use Windows 10 OEM key, you can't reuse it. You can buy cheap Windows 10 Pro key here: [URL]
I bought a laptop from my company and change the SSD to a bigger one. Delete the company OS and install Windows 10 but it is not activated. How can I reuse the original license?
windows activation