Error 0x8004FE21 — This computer does not use a genuine Windows system

Error 0x8004FE21: This computer is not running genuine Windows

This error occurs in: Windows 10, Windows 11, Windows Server.

Cause

The system has detected that the installed version of Windows is not genuine — this may be due to modification of system files by malware, installation of language packs not available in the given version, or damage to system files.

Symptoms

• During activation, the message appears: "This computer is not running genuine Windows"
• Error code: 0x8004FE21
• English version: "This computer is not running genuine Windows"

Step-by-Step Solution

Download and run Windows Defender or another antivirus program. Then, download the original Windows image from Microsoft and reinstall the system. Contact the seller if the system was pre-installed at the factory.

Solution for Windows Server

1. Open PowerShell as administrator
2. Enter the key:

slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

1. Activate:

slmgr /ato

1. Check the status:

slmgr /xpr

Verification

After performing the steps, check if the activation was successful:

• Windows: Settings → System → Activation → should be "Windows is activated"
• Or: slmgr /xpr in the command line

Still not working?

If the above steps did not help:

1. Check the date and time — they must be correct (an incorrect date can block activation)
2. Temporarily disable antivirus and try again
3. Check the internet connection — online activation requires a connection to Microsoft servers
4. Contact us:
   • Email: [email protected]
   • Phone: 00 800 121 1654 (toll-free)
   • Help center: pomoc.kluczesoft.pl