I sold my computer but forgot to deactivate Windows(box)

[drewny]

A few years ago I bought Windows 10 home box version.
I had Windows installed on a computer that I sold half a year ago and I didn't know that Windows had to be deactivated from the computer.
Today I wanted to use the license and I received error 0xC004C008
I didn't have Windows assigned to my Microsoft account.
What can I do in this situation?

[#2]

Reach out to the person who purchased your computer and explain the situation. They might be willing to deactivate Windows on that device so you can reuse the license. Explain your situation to Microsoft Support. They might be able to help you deactivate the license from the old computer remotely so you can activate it on a new one.

[#3]

If you have the original product key, provide it to Microsoft support. If you purchased Windows 10 Home as a retail box version, the product key should be on a sticker inside the box. And, Microsoft support should be able to assist you with deactivating the previous installation of Windows associated with your product key and helping you activate it on your current computer.

[#4]

@drewny Explain the situation to Microsoft Support. They might be able to help you transfer the license to your new computer, especially if you can provide proof of purchase for the Windows 10 box copy. You can find contact information on the Microsoft website.