Start with the right checks.
An activation message can follow a hardware change, reinstall or edition mismatch. It does not automatically mean that another purchase is needed. Keep the original purchase and setup information available.
What to do next.
Open Settings, System, Activation and record the activation status and exact error.
Check whether the installed edition matches the license supplied with the PC or purchased separately.
If a Microsoft account was linked to a digital license, use the intended account and Microsoft’s supported troubleshooting guidance.
For a business device, ask the administrator or original supplier to confirm the license arrangement.
Check the result.
Check that Settings reports the expected activation state. Keep the record of the legitimate license and any change that resolved the issue.
Stop and get help if…
The PC was sold with an unclear license, an edition change is being proposed or activation still fails. Buying a second subscription or cheap key without checking the cause can create another problem.