Hi,
Do you have a retail license, and did you reinstall Windows on that HDD/SSD only to find it isn't activated?
Is it a digital license?
Or
Did the license you have come from a free upgrade from Windows 7 or 8/8.1, or directly from Windows 10 to 11?
Did you try activating it after a hardware change?
https://support.microsoft.com/en-us/windows/activation/reactivating-windows-after-a-hardware-change
Thanks.