murag dili man tingali na pwede, if you change your processor or motherboard after you have activated your windows license, it becomes invalid.
before kato mga windows xp, i know there was a certain kind of license nga transferable... i dont know karon if that kind of "transferable license" still exists sa windows 7/8.
or you could always go to a certified microsoft reseller like NG KHAI and ask them about it to be sure.
and about your question about power consumption sa nvidia vs amd is too broad. it should be a specific nvidia model vs a specific amd model. its like asking "asa mas kalas og gasolina, toyota or mitsubishi?" nobody can answer that
