Yes, you can use a Windows key from an old computer.
Yes, you can use a Windows key from an old computer.
When RaptorCandy mentioned: If the version you possess is an OEM release, it won't work. But if not, you're in the clear. I believe the sticker should clearly state whether it's an OEM model. Alternatively, if you can boot your old PC, in the "System" section under "System and Security" in the control panel, the product ID of the installed Windows software should appear. If it displays "OEM" after the initial digits, that confirms it's an OEM version.