HP Pavilion DT 500-164. After utilizing Win10 since the initial offering. Microsoft yesterday, after a clean install decided that it was not activated. Today I updated to 10567. The long shot dream was that it would auto activate. The error code altered slightly with an explanation that will be summarized as follows: "Previous version of Windows not activated prior to upgrade to Windows 10." Running a Sony VAIO also with Win10. No issues, yet... There have been some issues with both computers as 10 evolved. But were resolved via a new download and either a USB or DVD install. My HP was difficult when it came to the USB boot as Legacy was enabled and UEFI was disabled in order to allow the USB boot. Once maybe twice I neglected to reset it back to secure boot. When I did remember to reset and then booted normally the HP posted: "...no operating system installed...install an operating system." Thus I would leave it as Legacy and it would update and run well. (Maybe not relevant. Attempt at leaving no stone unturned.) For the first time since I got my first PC, (4 yrs ago) decided to call Microsoft. Some of the Win10 help screens/forums/insiders etc. suggested that. After terminating several calls with no resolution. Would then call back in an attempt to make contact with competence, activation or even just an explanation. This is what I was told via those calls: 1. "Call HP they can fix everything." 2. "I will activate please hold." she neglected to say for how long fairly certain she took a lunch. "No I cannot activate." and upon my response of "why?" the phone connection was lost. Please be assured I didn't hang up. The next rep spent some time with me. Mostly it involved dictating various commands that I entered into the command prompt. He asked for the activation code that I've had since converting to Win10 but I could not locate it since the clean install wiped all clear. It was activated prior as I had checked. There was no mention of any utility that might locate it. Finally his answer was to "just purchase the activation code." Also, upon completion of the clean install the HP has a new name and new numbers that follow the name. More research today and I hope there is an activation issue on the Microsoft side. Doubt it. But I've become somewhat desperate. Also would like to avoid the DeeX posted solution in these forums if possible. Seems a little hasty to bring back an old operating system in order to get the current one. Never the less I'm open to any suggestions. Thank you in advance for your anticipated response. Sorry to be so long winded.