I recently bought windows 8 using the upgrade offer. Now I am planning to upgrade my computer ie , change the motherboard , processor and the Ram. I would like to know if i can use the same product key or do I have to buy another product hey for Windows 8 for the new configuration.
If you installed Windows 8 previously on the old machine, and after that if you change the motherboard and activate it it may some times fail. Your key is uniquely tied with your hardware. In such a case just call Microsoft and explain the issue. They will give the unblock code. So dont worry.
The answer depends on whether you have OEM or regular license to Windows version you're upgrading.
And now upgrade to Windows 8.
Your upgrade key is not tied to hardware. You can transfer the upgrade to another computer as many times as you want. The only requirement is that you have a previous version of Windows installed and activated on that computer. (Of course, you can still use it only on one computer.)
So if you have a regular license for previous version of Windows, you can safely upgrade. Yet either install the new hardware while you're using the previous version and re-activate it and then upgrade to Window 8, or upgrade on the current hardware, activate Windows 8 (should be done automatically) and then install the new hardware to your computer.
If the case of OEM version, it's not as clear.
Technically you can upgrade, just change the hardware after you upgraded to Windows 8.
Your previous version of Windows was running on the hardware it's tied to. You upgraded it to Windows 8 which license is not tied to particular hardware. Therefore you can change the hardware when your new Windows 8 is running on your computer. However, to re-activate it you will need to call Microsoft.
It depends on which license you have. They differ depending on whether you originally bought your Windows license separately or or if it came pre-installed as an OEM license. You can search for the EULA for any Microsoft product here.
Windows bought separately
If you bought your license separately, you may transfer your license to another machine that belongs to you. That would certainly include the same machine, merely upgraded. Here's what the Windows 8 English EULA says:
As Bala states, if you're transferring your license as the EULA allows but your code doesn't work because you've used it before, call Microsoft and they'll give you a new one.
But if your original copy of Windows came pre-installed, you're covered by their OEM license, which ties the license to that particular machine. Here's what the Win7 OEM license says:
As stan31337 reports, Microsoft's position is that this means you cannot change out the MB.
I am not an attorney but I am not convinced that Microsoft's interpretation of their own EULA would actually hold up insofar as the EULA does not actually state that you can't repair or upgrade the machine, both of which of seem to be reasonable things that consumers expect to be able to do unless explicitly denied. Otoh, if they refuse to activate your license, they win unless you're willing to sue them, which seems unlikely unless you could find an attorney willing to take it on a class action.
The installation will work so long as it sees another previous Windows installation (Windows XP or up). The product key is not dependent on hardware as far as I know. Just be sure to retain the hard disk you had your previous Windows install on.