What exactly does a product key license?

Hi, folks!
I hope to get some clarification for my issue about reinstalling a copy of Windows 7.

I am about to install Windows 7 Home Premium 64bit on a flash drive and I wonder if I can simply reuse my current product key. I am aware similar questions have been posed lots of times but hear me out, please.

According to Microsoft, I can use my product key only for one pc at one time. But how do they know when I want to activate my installation of Windows 7 and that the former one does not exist anymore - won't the activation server think that I am using the same product key again for an additional system?

There are commands to remove the current product key from one's system, but that prodecure won't get noticed by Microsoft, right? ...even if I format my current drive where Win7 is installed.

Edit: To be clear about the title... does a product key activate the current copy's product-id or what exactly gets licensed?

So how do I make sure that current product key can be used again without any issue about licensing and stuff?

thanks a lot!

This depends on a few factors. 1 is if the PC in question is an OEM PC....meaning a purchased retail PC that windows came preinstalled on. Then the answer is No because that PD Key is tied to the mobo permanently...meaning it can't be transferred.

If a retail copy of the OS then Yes, you can transfer the Key to any mobo you like. Provided that the OS is removed/uninstalled from the previous system.

The product key is what MS allows you to use the OS, it is what activates the OS through MS. Since windows 7, MS activation has a 3 day window to activate (used to be 30 days) or you'll experience intermittent shut downs and or reboots. Basically you're paying for the Product Key and leasing the OS according to the EULA (simplified of course).

Thanks a lot for your quick reply!

My machine is a custom build from 2010 and I purchased a dvd including a valid product key from a local retailer.
So, you say I can use my product key on any system as long as the current operating system's copy is removed from my machine. But this is where my question starts! Doesn't Microsoft need to know that I removed it? How could they know if I simply format my hard drive?

Perhaps this is easier than I expect but I want to be completely clear before I do anything severe ^^

Yes....I do it all the time with my retail keys.

As to how MS knows the previous install has been removed/uninstalled is just as mysterious to you as it is to me. I think it has to do with it being used and not used (Product Key) during activation. If used and some one tries to use said same key, you get the error message "invalid key".

Ms keeps a data base of keys being registered....for OEM, Retail and Key volume installs (big business, schools, Inc. and the like).

Well, this sounds pretty good so far!

But in another scenario, if I will get an entirely new pc in some time, how can use my current product key then? I expect there must be some procedure to reverse the activation process (or at least remove the current one) in order to use the prodcut key on a different system.

thanks again for your time : D

Yes you can....all you do with the previous system is wipe the drive clean (format).


Extraordinary Member
There may be conflicts e.g. when your hardware died and you now want to use the OS key on a new build. In that case you call Microsoft and ask them to sort it out. Here are the phone numbers of the worldwide MS activation centers.



Extraordinary Member
Premium Supporter
The copyright issues are altogether very difficult. If I have the correct picture, Windows XP was the first where you could change a CPU, without reinstalling the whole system. I would recommend what whs says: call Microsoft. It's hard for me to understand that people don't want to call them, if they have a legitimate cause. I've called them half a dozen times, and it's all worked just swell. And my Windows 7 has worked fine for a couple of years. Might have cost me a couple of bucks... but my PC works.


Fantastic Member
Premium Supporter
To organize and explain it a little better.

1. If it is a store bought (OEM PC). If for some reason you need to reinstall Windows. As long as none of the major components inside have been changed (Motherboard, Hardrive or SSD and CPU) you can just use the license key on the back of the system to reactivate Windows.

2. If on the other hand you due a major upgrade to said OEM PC which causes the Installation ID to change you will need to contact a Microsoft Activation Center. Explain why you need to reactivate windows (IE had to change my motherboard due to failure) they will take some information from your new installation ID deactivate the old installation ID and activate your new installation ID.

3. If it is a custom built PC basically it is the same deal you will need the Product Key from the DVD. I have built many a custom PC for myself I have not bought a full version of Windows since XP. I always get the upgrade versions which you can not activate on a clean install there needs to be a full version of an older OS installed while it is not like I am going to install XP then try to install 8.1 so I call Microsoft every time I need to reactivate Windows and they always help me out.

4. To summarize it if you can not get Windows to auto activate give Microsoft a call explain why you need it reactivated and they will take care of it.

Also here is link to FAQ for Windows 7 activation http://windows.microsoft.com/en-us/windows/activating-windows-faq#1TC=windows-7

This website is not affiliated, owned, or endorsed by Microsoft Corporation. It is a member of the Microsoft Partner Program.