if you take a hard drive from another computer and put it in a different computer, you usually have to re-activate windows since the oem license no longer matches the one in the bios on the motherboard.
All prebuilt computers, like dell, hp, etc have OEM windows license which are only good for the computer they came on (the motherboard which came with that computer).
By transferring your hdd, and that windows installation, to a new computer (motherboard), you invalidated your windows license, and you get 30 days to activate it. (maybe less im not sure of exacts), so you have that amount of time to get a windows license key or you will be locked out of your windows os.
The only way is to go buy a new windows xp key (which would be dumb since xp is like no longer supported, and it would cost the same price as a new windows 7/8 os), or you will need to keep reinstalling the windows os every 30 days.
it has nothing to do with adding a new graphics card.
and the barebone kit is just the hardware, you need to purchase windows separately.
and you didnt purchase a retail windows license.
You either bought a computer (like dell,hp etc) which came with an oem windows license for THAT computer, or you bought an OEM windows license yourself and put it on ONE computer (which it states that right in the license statement for OEM versions of windows).
there is a reason OEM windows is cheaper then retail. Its because retail you can install it on a different computer when you are done using it, OEM you can not.
its like saying you bought a day pass to a amusement park, and come back the next day and complain your day pass no longer works, and you should be allowed to use it because you purchased a ticket...
Now if you are 100% sure you bought a "retail" version, and because you bought a copy of windows doesnt mean its a "retail" copy. it has to actually say "retail" on it. Then you can reinstall it on another system.
now if you lost your cd key, thats a problem. Because you are paying for a license, not the disc itself. You can download the disc from microsoft for free, but you need to PAY to activate it within 30days.
If you have some proof of the purchase of the retail version, you can probably talk to the microsoft support.
If you have no license key, and no proof of purchase, then you do NOT own that copy of windows.
its like going to the store to exchange something with no receipt.... they arnt going to do anything for you... as far as they are concerned, no proof of purchase means you stole it.
and dont be like "microsoft is bullshit" or something because of this, as though they are an evil greedy cooperation and w/e, but EVERY SINGLE THING IN THE WORLD, works in this SAME EXACT way.
if you have no proof of purchase, you do NOT own the item. period.
and if you have an OEM license, then thats what you agreed to. Take it up with dell, hp etc for not giving enough clarification that your windows license is an OEM license.
And if you knew you bought an OEM license, but didnt understand the conditions of it, that is YOUR fault.
hopefully you will learn to actually READ things before just buying or accepting terms. There was a southpark episode that was really great on this subject about just clicking "agree" to everything w/o reading it. Now ya you may not have to read the every single thing start to finish, but when you get screwed, you have no one but yourself to blame.
And with buying or using something, if you dont fully understand it, ask. most things you can buy or download, have a support section to contact the developers/creators/manufacturers, and they also usually have a forum section to ask questions.
And on top of that, there is... the internet, which not only can you usual find anything you need to know just by searching, but you can also ask on many different sites and forums aswell.
just because you are too lazy to do it....
EDIT: well i explained it rather well i think.... and for some reason you STILL dont get it? really?..... stupid people are stupid....