Windows 8 says my product key is is currently being used by another computer?

Try to use your key for activation through the procedure I have described in this link:

I found this answer earlier but when I tried it I go to location and do not see "MediaBootInstall". Here is what I see:

Then you can activate windows through phone. Here is the procedure:

I found this answer earlier but when I tried it I go to location and do not see "MediaBootInstall". Here is what I see:

(Default) - REG_SZ - (value not set)

SetupDisplayedEula - REG_DWORD - 0x0000001

SetupDisplayedProductKey - REG_DWORD - 0x0000001

SetupStartedBy - Reg_SZ - My_Name

How To Activate Windows 8

Windows Product Activation (WPA) sends an installation ID number to Microsoft before Windows is verified and then activated.

One is an Installation ID, generated by entering a Windows 8 product key, that the computer owner submits to Microsoft, either over the Internet or by phone.

The second is a Confirmation ID, assigned by Microsoft, which is used to activate the operating system’s software.

Activate Windows 8 Using Internet

The easiest way to activate your Windows 8 is to activate it over the Internet. To start the Product Activation Wizard, follow these steps:

1. At the Start screen, swipe in from the right side, or hover your mouse in the upper-right corner of the screen to display the charms menu.

2. Tap or click the Settings charm.

3. Tap or click Change PC Settings.

4. Select Activate Windows (If your Windows is activated successfully, you will not see Activate Windows in the PC Settings)

5. Tap or Click Activate.

6. Enter Product Key.

The product key should be printed on the box that the Windows 8 DVD came in or included in an email you received after buying Windows.

7. Windows will now automatically detects whether the product key is valid. If your product key works, clickActivate .

8. If Windows Activation is successful, click Close.

If activation was not successful, check the key and try entering it again.

Activate Windows 8 Using Phone

If your are unable to activate Windows 8 over the Internet then you can contact Microsoft by phone to activate the product. You do not need Internet connection to activate Windows 8 over phone.

To start the Product Activation Wizard, follow these steps:

1. At the Start screen, swipe in from the right side, or hover your mouse in the upper-right corner of the screen to display the charms menu.

2. Tap or click the Settings charm.

3. Tap or click Change PC Settings.

4. Select Activate Windows

5. Tap or click Activate by phone.

6. Select the country/region from the drop down menu, and then click Next .

7. Call the toll free number provided.

8. Follow the instructions from the telephone system and write down the confirmation ID.

9. Enter the confirmation ID numbers into fields A through H, in the same sequence as the telephone system provided them. When done, clickActivate .

If product activation was successful, a success screen is shown and you are done.

Yeah, I already did that. Like I said above, it claims this key is already being used on another PC. I've only used it on this computer and I got it through a confirmation email from Windows the day I purchased it. It says"

Does not work. Automated Windows robot says that the key is being used on too many computers. This is the only computer I have used it on. No hardware or software changes. Does not give me option to talk to someone in person. Just hangs up after saying "Sorry, your Windows key is being used for more than what it is licensed for." 

The exact same thing is happening to me. The automated message just says I my key already used and hangs up on me. What is this bullshit? All I want is to use my computer and software I paid for. 

I'm having the same problem. However, luckily for me, it would normally go away after a reboot. But it would frequently re-occurs again and again.

Yes! I have the same problem.
I have:

Reinstalled Windows 8.1 , entered the license key which checks out in the beginning of the install,
the end of the install and everything works.

Hours later, I keep being redirected to the 'Change PC Settings' to 'activate Windows'.

If you go there, it tell you that your license key is being used on another computer;
Well it is NOT being used on another computer!

So, Microsoft, how do we fix this error. Where do we go to delete an incorrect log file, or whatever? I called Microsoft and it was a joke. No one could help me. Are we saying support has no idea of this is current issue?

This should be something that can be resolved easily. We all shouldn't be here floating in the middle of the ocean waiting for someone to find us.

My guess is that your Windows Key was leaked by "someone" and multiple people used it to activate their Windows installation. This may happen if you (or someone else) shared the key on a discussion forum or gave it to a local support technician who leaked it further.

We should have at least this faith in Microsoft that their log files are not incorrect. That's what my experience & understanding is.