I assume you discovered your license for Windows is not a full Retail license and therefore is not transferable. For others who may stumble on this this thread, it is illegal to use a Windows license that came with, or was bought for another computer. If the disk says OEM/System Builder, Upgrade, Academic Edition, or "For Distribution with a new PC only", then it is not transferable to a new PC (or upgraded motherboard - which is considered a new computer). Only full "Retail" licenses can be transfered to new computers. Therefore, a new Windows license must be purchased, or use one of the many free Linux alternatives.