|OK. The computer crashed, and upon reboot, did not work? I'm trying to make sense of this...|
The product key (if an OEM or retail package) will not be of any use, if the disc is not with the product key. If you have a disc, however, you can press R once you've booted into the disc's environment, and repair Windows from there.
However, if you really need to reformat or restore the computer, I would highly recommend downloading and installing Linux. You can download LinuxMint from here: http://www.linuxmint.com/download.php
Contrary to popular belief, Linux *does* run a lot of its own programs, and Windows programs as well. To run Windows programs in Linux, you can install Wine or you can even emulate Windows inside Linux using VirtualBox. Running Windows programs in Linux just takes more work, which is why it is not liked as much as Windows is. It is a really good system, and highly recommended, as it is legal like Windows, yet Linux is completely free. However, please note, I'm *only* recommending it. If you need Windows, go to the Microsoft Store and purchase a copy of Windows 7 to install and upgrade Windows on his computer.