Windows activation error 0xC004C008: Product key already used on another device
Updated
Cleared for publishing after the automated checks on .
What these 3 codes mean
This page covers 3 codes: 0xC004C008, 0xC004C770, 0x803FA071.
0xC004C008: Product key already used on another device
The activation server determined that the specified product key could not be used. (Troubleshoot Windows activation error codes)
0xC004C770: Product key already used on another device
Listed with 0xC004C008 in Microsoft's activation help row: the key was already used on another device or on more devices than the license terms allow. The steps are on the 0xC004C008 entry.
0x803FA071: Product key already used on another device
Listed with 0xC004C008 in Microsoft's activation help row: the key was already used on another device or on more devices than the license terms allow. The steps are on the 0xC004C008 entry.
Code facts
0xC004C008: Product key already used on another device
| Code as Windows shows it | 0xC004C008 |
|---|---|
| Type | Activation error code |
| Hexadecimal, 8 digits | 0xC004C008 |
| Decimal (unsigned) | 3221536776 |
| Decimal (signed 32-bit) | -1073430520 |
| Group | Activation errors |
Read with care
- Not a standard HRESULT (R bit set without the N bit, MS-ERREF 2.1). Microsoft lists it as a Windows activation (Software Protection) code; do not split it into facility and error number. ([MS-ERREF]: HRESULT, Troubleshoot Windows activation error codes)
0xC004C770: Product key already used on another device
| Code as Windows shows it | 0xC004C770 |
|---|---|
| Type | Activation error code |
| Hexadecimal, 8 digits | 0xC004C770 |
| Decimal (unsigned) | 3221538672 |
| Decimal (signed 32-bit) | -1073428624 |
| Group | Activation errors |
Read with care
- Not a standard HRESULT (R bit set without the N bit, MS-ERREF 2.1). Microsoft lists it as a Windows activation (Software Protection) code; do not split it into facility and error number. ([MS-ERREF]: HRESULT, Troubleshoot Windows activation error codes)
0x803FA071: Product key already used on another device
| Code as Windows shows it | 0x803FA071 |
|---|---|
| Type | HRESULT (Windows result code) |
| Hexadecimal, 8 digits | 0x803FA071 |
| Decimal (unsigned) | 2151653489 |
| Decimal (signed 32-bit) | -2143313807 |
| Severity | failure |
| Facility | 63 FACILITY_WINDOWS_STORE |
| Group | Activation errors |
Read with care
- Facility 63 (FACILITY_WINDOWS_STORE) is only in the SDK facility list; the MS-ERREF facility table does not list it. (HRESULT_FACILITY macro (winerror.h), [MS-ERREF]: HRESULT)
Code facts: Troubleshoot Windows activation error codes (Microsoft Learn, CC BY 4.0), checked Nov 14, 2026.
Where this error shows up
This code shows up when Windows tries to activate or when the product key is checked.
Applies to
- 0xC004C008: Windows 11 (steps taken from the page's Windows 11 section; the page has a separate Windows 10 section where some button paths and steps differ).
- 0xC004C770: Windows 11 and Windows 10 (activation help page has a tab for each)
- 0x803FA071: Windows 11 and Windows 10 (activation help page has a tab for each)
Try these first
These steps carry no risk flag in the data. They keep the order of the full list below, which is not reordered. A step without a flag is not a promise that it is safe for your computer.
5 steps to try, in order
Steps are grouped by the Microsoft page they come from. The page lists only what those pages give; other causes of 0xC004C008 are not covered.
If this page and Microsoft's page differ, follow Microsoft's page.
From: Get help with Windows activation errors
Source: Get help with Windows activation errors (Microsoft Support), checked Nov 14, 2026. Summary in our own words; Microsoft's page has the full steps.
0xC004C008: Steps follow the Windows 11 tab of Microsoft's activation help page; its Windows 10 tab has its own version of this row (Windows 10 support ended on October 14, 2025).
One key per device
Each device needs its own product key: buy one for every device you want to activate.
Buy Windows from the Microsoft Store
Go to Start > Settings > Update & Security > Activation (the path as this row prints it), select Go to Microsoft Store and follow the steps to buy Windows 11.
No Go to Microsoft Store button on the Activation page? Ask your organization's support person.
After a big hardware change, activate by phone
If you swapped major hardware such as the motherboard and still hold a valid product key, activate by phone: type SLUI 04 in the taskbar search box, select SLUI 04 and follow the on-screen steps (Microsoft's 'Reactivating Windows after a hardware change' page has more).
Windows 11 Pro EDU and Windows 11 Pro for Workstations can only be activated online; neither phone activation nor SLUI 04 works for them.
From: Troubleshoot Windows activation error codes
Source: Troubleshoot Windows activation error codes (Microsoft Learn), checked Nov 14, 2026. © Microsoft, licensed under CC BY 4.0. Steps shortened and reworded by PC Driver Update.
0xC004C008: Microsoft's volume activation (MAK/KMS) error page, written for technical support agents and IT professionals.
KMS host key limit reached
For 0xC004C008.
Written for IT administrators.
The KMS key has exceeded its activation limit (KMS host keys can be activated up to 10 times on no more than six different computers). Contact the Microsoft Licensing Activation Centers to request more activations.
From: Error 0xC004C008 "The specified product key could not be used" when you activate Windows
Source: Error 0xC004C008 "The specified product key could not be used" when you activate Windows (Microsoft Learn), checked Nov 14, 2026. © Microsoft, licensed under CC BY 4.0. Steps shortened and reworded by PC Driver Update.
0xC004C008: Microsoft's page for 0xC004C008 with a KMS host key; written for IT professionals, applies to Windows client, Windows Server and Azure VMs.
Get a new key or reset the activation count
For 0xC004C008.
Written for IT administrators.
A KMS host key can be used for up to 10 activations on a maximum of six computers; past that it is flagged.
To get a new key or have the activation count on the existing key reset, contact Microsoft Volume License Key assisted support (requesting more KMS host activations needs the VL Administrator or Product keys reader role). You can also request more activations through the Microsoft Engage Center request form with the agreement or enrollment number or license ID, the product name, the number of host activations needed and a business justification.
For Azure VMs that don't need a self-hosted KMS key, the page's Step 2 switches the VM to Azure KMS.
Stop and get help
If these steps do not fix the problem, or you are not sure about a step, stop and get help from Microsoft Support or from the maker of your PC. Stop at once if the data on this computer is at risk: back up your files first, or ask a professional before you go on.
Dates and review
| Automated checks | first check: ; second check: ; third check: ; fourth check: |
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| Microsoft pages read |
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| Review status | Cleared for publishing after the automated checks on . |