Hi,
Did you changed any hardware such as motherboard, hard disk and other mainly part of this device?
As system activation is based on your hardware ID, once you have changed hardware of activated device, Microsoft activation server will regard this device as a new one and require to activate it again.
Try to run "slui.exe 4" in command prompt as administrator to activate it through a call.
We also could try to run "slmgr /ato" as administrator in cmd to activate again to check.
Bests,
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