There are ways of using the installation on a new computer by doing a repair installation, and after the first restart hard shutdown, remove it from old pc and then insert it into the new pc. In terms of the activation, it will depend on the licence you have. For example OEM means one computer, however I have called MS many times and they've given me a new activation code.
The best option though, is to re install Windows, all your drives and updates. Then try to activate. If unsuccessful, call them, you'll get activated for sure. Then copy your files over.