0xC004C770 Activation Error: Key Already Used on Another Device

The 0xC004C770 activation error says Microsoft’s servers already have this product key on record for another device. The key is real. It’s just counted as taken.

Typing the key again won’t change the answer. The server gives the same reply until the record changes on its side.

What 0xC004C770 stands for

Microsoft groups the code with two others on its activation errors page. They share one explanation.

• The product key has already been used on another device.
• Or it’s used on more devices than the Microsoft Software License Terms allow.

The fix Microsoft gives is blunt: a product key for each of your devices. One exception follows right after it, and it matters.

After a substantial hardware change, with a valid key in hand, Microsoft sends you to phone activation. A new board looks like “another device” to it.

Causes

How to fix the 0xC004C770 activation error

Work out where the key lives now. The steps follow from that.

1. On the PC that used the key before, open Command Prompt as administrator and run the two removal lines.
2. Restart that PC; its Activation page should now say Windows isn’t activated.
3. On the new PC, open Settings, System, Activation, Change product key, and enter the key.
4. If it’s still refused, press Troubleshoot on the same page and follow what it offers.
5. If the troubleshooter doesn’t help and the key is yours, start phone activation.
6. Read the installation ID to the automated line and type the confirmation ID it gives back.

slmgr /upk
slmgr /cpky
slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
slmgr /ato
slui 4

Removing the key on the old PC doesn’t always clear the server record at once. That’s what the phone route is for.

The old PC is gone

Sold, dead or recycled. You can’t run anything on it, and you don’t have to.

Go straight to step 3 on the new PC. If the key is refused, phone activation is the next stop, with the same key.

The automated line asks how many computers the key is installed on. The honest answer is one, this one.

We wrote up the whole move and the rules per license type in our guide to transferring a Windows license to a new PC.

Same PC, different hardware

You never moved the key. You replaced the motherboard, or the board and the processor, and reinstalled.

That case often shows up under another number. We cover it in detail under 0xC004F211.

The key was never on a PC of yours

Fresh purchase, first try, and the server says it’s taken. Then someone else got there first.

That happens with keys from auction sites and anonymous marketplaces, where one code is sold to several buyers. Nothing on your PC fixes it.

• Write to the seller with the code and a screenshot of the Activation page.
• Ask for a replacement key, not for instructions.
• Don’t accept “activators” or remote sessions as a fix.

Need one that hasn’t been anywhere? Our keys are genuine, sold once and arrive instant to email: Windows 11 Pro and Windows 10 Pro.

Why some low-priced keys end like this is explained in Retail vs OEM vs Volume license.

Its two sister codes

Microsoft explains the first three with the same sentence, so the steps on this page apply to all of them. Other numbers are in our list of Windows 11 activation errors.

Where these steps apply

The key field and the status lines are shown in how to activate Windows 11. Lost the key itself? Our ShowKeyPlus guide reads it from a running PC.

Mistakes we see most

• Entering the same key ten times in a row.
• Leaving the key active on the old PC “just in case”.
• Using one retail key for two computers at home.
• Skipping the phone route because it sounds old-fashioned.
• Paying a stranger for a remote “fix” of a key that was sold twice.

Terms used on this page