Cannot activate windows, must upgrade windows 10 pro to windows 10 pro

My Windows 10 pro suddenly got deactivated.

Why?

When I go into settings and Activation Settings in windows 10 pro, I get a message reading

Edition Windows 10 Pro Activation Windows is not activated

We can't activate Windows on this device as the product key you entered doesn't match the hardware profile. If you recently repaired Windows or made significant hardware changes to this device, select Troubleshoot to try and fix the problem or go to the Store to buy genuine Windows. Error code: 0xC004F034.

So I click that link and a dialog comes up that after a couple of seconds. It sais

Troubleshooting has completed

We found a Windows 10 pro digital license for this device running Windows 10 Pro. To activate using this digital license, select upgrade your edition of Windows.

I clicked the link, the dialog shows the text

Upgrade your edition of windows This might take a while. Don't turn off your PC. 0% complete.

...but the dialog closes after a couple of seconds, the percentage still being 0%. The computer restarts. Nothing more happens. If I enter the Activation settings, nothing is changed.

• I have not done any significant hardware changes (half a year ago, I bought two new hard drives).

• The windows 10 pro version I have is an upgraded Windows 7 from the time where there was an offer to upgrade windows 7 to windows 10 freely.

So I need to upgrade windows 10 pro to windows 10 pro?

What is that?

Something went very wrong with Windows. I suggest:

1. Check the disk SMART data for degradation
2. Run chkdsk
3. Run sfc /scannow and the DISM command in the link
4. If all fails, do the "upgrade" by Repair Install of Windows 10 with an In-place Upgrade.