Can I overwrite Windows?

[Teedo]

So as of now I have this complete sh*t setup an I'm basically updating the whole computer..

I have bought a new motherboard, new ram, cpu, dvd drive, cpu cooler etc..
(Not to get off topic)

Anyways, I didn't purchase a new HDD (because I already own one) and didn't purchase Windows. Now I was wondering if there's a possible way I'm able to download windows on my pc.. (That I have now, store onto a USB) then when computer is built use the USB to boot Windows an bypass the Product Key because Windows is already on the HDD?

So basically my pc came installed with Windows 8.1 then upgraded to Windows 10. Can I build my new PC an run Windows from the HDD I already own or can I boot Windows from a USB an downgrade my Windows 10 back to Windows 8.1 without being prompt with a Product Key screen?

Or is there possible a way I can find my Windows Product Key on the current PC I have to reinstall on my new PC with the Product Key and same HDD?

On Microsoft's website before Downloading the Download Tool for Windows 8.1 it say's

If you will be installing the operating system for the first time, you will need your Windows product key (xxxxx-xxxxx-xxxxx-xxxxx-xxxxx). For more information about product keys and when they are required, visit the FAQ page.

So if using the same HDD that I have now.. Am I able to reinstall Windows on my new PC using a USB an same HDD an not be prompted with a Product Key window?

sorry if this is hard to understand.. lol.

 

[USAFRet]

A reinstall of the OS will require you to enter the license key. There is no way around this.

You needed to discover your license key for your OS before you did all that hardware change.

Put the PC back together with the old hardware.
Does it boot up?
If so, install Belarc Advisor
Run it
Discover your 8.1 license key

Go to that MS site, enter that license key.
If it lets you pass, OK. Download the ISO and create a DVD or USB install.
If not, you have an OEM license, and you are kinda screwed.

 

[USAFRet]

A new motherboard will trigger re-entry of the license key.
A new motherboard may require a new OS install.
A new motherboard may require a new OS purchase, depending on what license it was originally. Retail or OEM.

 

[Teedo]

A reinstall of the OS will require you to enter the license key. There is no way around this.

You needed to discover your license key for your OS before you did all that hardware change.

Put the PC back together with the old hardware.
Does it boot up?
If so, install Belarc Advisor
Run it
Discover your 8.1 license key

Go to that MS site, enter that license key.
If it lets you pass, OK. Download the ISO and create a DVD or USB install.
If not, you have an OEM license, and you are kinda screwed.

I'm currently still using my old PC.
I haven't built it yet...

But there is a way to find out my Product Key on my current PC?
An if so am I able to reuse that Key?

 

[USAFRet]

I'm currently still using my old PC.
I haven't built it yet...

But there is a way to find out my Product Key on my current PC?
An if so am I able to reuse that Key?

This depends on what license it is, Retail or OEM.
Retail, yes. OEM, no.

Belarc Advisor can discover this license key.


But...your new PC needs its own license.
If nothing else, it needs a full reinstall of the OS, not just plugging your old drive in and hoping it just boots up.

 

[zarawatsonn]

It is a rule under Microsoft guidelines, if you change your hardware, then your copy of Windows is not consider as a Genuine Copy.