If you have a full retail version of Window 7, you Can re-use it...
If you have an OEM version, like Dell, HP, Gateway, it's keyed to their hardware and can't be re-used....
If you have a OEM/Builders version of the OS, it will not allow you to use it on a new motherboard
- I have tired this, twice, going Intel to Intel
- In one case ONLY changed the motherboard to a "very slightly different" ASUS motherboard
- call Microsoft and they confirm while you can boot-n-load, you can not register re-use the copy on the new board
Here is their License Agreement:
Disclaimer: Use of this OEM System Builder Channel software is subject to the terms of the Microsoft OEM System Builder License. This software is intended for pre-installation on a new personal computer for resale. This OEM System Builder Channel software requires the assembler to provide end user support for the Windows software and cannot be transferred to another computer once it is installed. To acquire Windows software with support provided by Microsoft please see our full package "Retail" product offerings.
Must be different in your experience................. or, you have a Full Retail version