Legality of installing Windows XP on another machine

Legality of installing Windows XP on another machine

Several years ago I bought a PC which came with Windows XP, now that PC nolonger has XP installed (Ubuntu instead). Is it legal for me to install XP with that serial on a different PC? The XP installation has never been used on the another computer. I have reinstalled XP a few times on the computer it came with after formatting.