If your copy of Windows is OEM, then it's tied to the motherboard and you will have to purchase a new license. If it's retail, then you are good to move it to your new system. What kind of success you will have moving it is hard to say as they may be significant driver issues that are easier to solve by starting fresh than attempting to troubleshoot.
Ok so ill keep my old comp for a backup maybe give to my friend..and ill just buy a new 1tb 7200 for space..im still not sold on the SSD yet..as im just strictly gaming..not worried about boot times. just to much money..
OEM well the system i bought at bestbuy 2010 came with the OS so that means OEM i imagine so:
Shall i buy windows 7 then upgrade to 10? whats the cheapest surest route to windows 10?