"This copy will never run out, and you can use as many times you want to on any computer/laptop. "
So it is an illegal copy then!
Chrisrob.
There are only a couple of different versions of the windows CD and license and the only ones you would have are either OEM or retail, all you need to do is find a CD of the same version and there shouldn't be a problem registering it with the key you have on the COA stuck to the case.
Look on the sticker on the case and if it's an OEM version it will say OEM on it, if it's a retail version it won't say anything other than the key number, which do you have?