do you want to move windows from one PC to another. If it is OEM it is likely to be matched to motherboard its installed on. what version of windows is it, as you might be able to move win 10?
or
do you want to move the hdd from one PC to another and use it as storage? Easiest way to wipe it is run http://www.dban.org/ on the hdd before you remove it from current PC. this will wipe it and mean it won't conflict with the other hdd with an os on it. You will need to run disk management on the drive once its in new PC as windows won't see it until its formatted