Win 8 won’t activate. Says “already being used on another PC Try a different key or buy a new one”

Has the key your using been used on another client? Is this windows 8 or windows 8.1, bear in mind the licenses are different for the two, so you cannot use a windows 8 key on a windows 8.1 client.

Also try opening the command prompt as admin then running

slmgr /upk

This will uninstall the current product key

then run

slmgr /ipk %productkey%

Then run

slmgr /ato

this will attempt to activate windows

maybe this may help with the above http://tweaks.com/windows/39026/change-windows-product-key-after-install/

Have you tried activating via Microsoft's telephone method? you may need to re-install Windows.

Basically the message means just what it says => Microsoft's activation records indicate this key was used on a computer with a significant difference in the system's hash code -- indicating it was a different PC.

If that's not the case, just call the telephone activation center and they'll provide you with a code to resolve this.    If it has indeed been used on another system, you'll need a new key.

reinstalled the OS which resolved the issue

Did you reinstall from the recovery partition or the recovery disk?

Or did you do a complete reinstall? If so did you use a different product key?

No, complete reinstall and I think techs used a different key