HP recovery dvd, can't activate Windows

I have purchased recovery disks for my HP pavillion computer. They install O.K. (a bit slow thanks to HP), But when trying to activate, I get the following error message= "The Windows Vista Ultimate product key you typed is invalid for activation". Can anyone explaine this to me, and why it happens. Thanks in advance.

You should be asking HP this question.

When Windows is installed on a PC by an OEM, they use a key that you do not see. The key that is seen on the sticker attached to the PC is NOT the one that the OEM uses. While it should work, in some cases, it does not.

So, as Cliff said, you need to contact HP to find out why the key in the sticker does not work.