I got a new hard drive and motherboard, have windows xp half installed (copied from old hard drive) but when I put the new hard drive onto the new motherboard it says I need to activate windows when I do that it says I have an invalid key code...any suggestions

This has happened to me before when I tried to clone a harddrive for a different PC with almost the same specs. It seems like windows will compile itself as a registered version on your drive but on a more secured place which I think you would be unable to copy. I reinstalled mine and just migrated the files right after.