Because I've never received any media(CD/DVD/USB/Download URL) from
Microsoft when upgrading from 7 Home Premium to 10 Home to 10 Pro nor
did I see any product keys from Microsoft for 10 Home or 10 Pro. The
only thing I received was the order history on my Microsoft account
that has the order number, date of purchase and the amount I paid for
Windows 10 Pro upgrade.
Your product key is connected to your hardware. Since you upgraded an OEM copy of Windows 7 Home, you received the rights to Windows 10 Home, which you upgraded to an OEM copy of Windows 10 Professional.
At this point if you wanted to install Windows 10 Professional you would just install it, since you don't have to worry about the installer finding the wrong key ( i.e. Windows 8.1 Core instead of Windows 8.1 Professional ), when ask for a license key you simply skip that step.
If I want to reinstall from scratch I have to start from Windows 7
Home Premium, then upgrade to 10 Home(which was free but isn't
anymore), then again up to Windows 10 Pro(using my purchased license
I've never seen). Which means, they said, I have to buy Windows 10
Home now to be able to reinstall from scratch.
You interpreted what they said incorrectly. You can indeed install Windows 7 Home, then upgrade to Windows 10 Home for FREE, since Windows 10 ISOs are 100% free. This is possible because your machine has had Windows 10 Home installed on it before. Of course doing this is a waste of time, since Windows 10 Professional was also activated on your machine, you can simply install that.
I can't burn ISO of Windows 10 Pro to a media and install it right
away because they said it's an "upgrade key" not full retail license
of Windows 10 Pro.
They gave you incorrect information. I don't know what question you literally asked them, it appears you are not clear how Windows 10 itself activates, so lets just move on.
ther rep said: my Windows 7 Home Premium key has been upgraded to
Windows 10 Pro key, and that I can use that key on the sticker on my
computer to install Windows 10 Pro from scratch via burned ISO on a
media.
This is false. A key to one version of Windows 7 cannot install an entirely different version of Windows 10. Windows 7 Home activated before the the offer expired, Windows 10 Home installations, that is all it activated.
Since your machine activation status is tied to a digital entitlement. You can only use a single installation of Windows on this machine unless you provide it an entirely different license key.
Any tool, you normally would use to determine your license key, will return a generic key. It's possible you can get the Windows 10 Professional key, after its been activated, again this will automatically happen since its tied to your
hardware.
if I want to reinstall Windows 10 Pro operating system from
scratch(without using Reset PC or Refresh PC, just please ignore this
option for now) what will I do when prompted for license during
reinstallation/activation phase?
You do understand that if you use the Reset feature, the end result is IDENTICAL, to formatting your machine and installing Windows 10 Professional right?
As for a program that might be able to get the correct key for your installation, the only key I have ever known to work, is ShowKeyPlus
I'm going to take a stab at this.
There is some important missing information in your question. Which edition of Windows 10 did you install?
Windows 10 will automatically activate using a digital entitlement that is stored on Microsoft's servers and it is recognized as belonging to your system by a hash of various hardware and software components. It is one of the nice new features about Windows 10 that eliminates keeping track of the product key. https://support.microsoft.com/en-us/help/12440/windows-10-activation
But, it won't automatically change editions. Instead, if Windows can find a matching digital entitlement, or a product key in the BIOS, it will activate with that. Otherwise, Windows will require you to enter a product key matching the edition of Windows that was installed. You need to re-install with the proper edition.
I'm assuming you downloaded your .iso using the Windows Media Creation Tool? If not, download it and use it so you have a proper Windows setup disk or usb drive: https://www.microsoft.com/en-us/software-download/windows10
If you follow the instructions below and Windows setup doesn't ask you which edition of Windows to install at Step 3, then you probably have a product key embedded in your BIOS. Here are instructions on how to modify the installation media so it will always prompt you for what edition of windows to install (thanks to Daniel B for pointing this out): http://www.intowindows.com/how-to-select-pro-edition-while-installing-windows-10/
To install with pro (or home):
- Boot the newly created disc or usb drive you made for Windows 10
- When you are prompted to enter a product key choose,"I don't have a product key." You might not see this step if you have an embedded product key in the BIOS.
- Next, you will be asked to choose which edition of Windows to install. Choose 'Professional' edition. If you don't see this, then modify your installation media as posted above.
- Complete the installation, Windows will automatically activate with it's digital entitlement if this same hardware has previously been activated with Windows 10 Pro.
This is how Windows works, and I'm confident Windows will activate automatically. However, if necessary, after being sure you installed Windows Pro (instead of home like you have), you can activate by entering any previous Windows 7 Pro, Windows 8 Pro, or Windows 10 Pro (even refurb) license key. Sometimes stickers for older license keys are still present on refurbished computers. As of the date of this posting, yes, you can still upgrade for FREE from a previous OS to Windows 10, and that will likely never change.
Changing only the hard drive will not impact Windows digital entitlement validity.
Best Answer
I searched from internet for quite some time and I decided to do the upgrade.
I entered the Windows 7 Pro production key again and accepted to do the version upgrade. It did the upgrade quite fast and it actually activated Windows.
Please note: this Windows 7 Pro production key was NEVER even upgraded to Windows 10, and I was still able to upgrade my Windows 10 Home to Windows 10 Pro with it. So everything is fine, the upgrade did not touch any programs / files (as matter of fact it only implented the Professional features).
Conclusion: I got 16GB RAM, better motherboard, better CPU, and upgradation to Windows 10 Professional, for free. I think it could not have gone any better?