The previous OS and files will remain on the hard drive you are replacing. If you install the OS, using the disk, on a new drive you will have to reinstall the programs and drivers you need. It may be possible to clone the drive and avoid having to reinstall all of the programs but that depends in part on how much space you need. As far as the key goes you may have to contact Microsoft if you have trouble activating windows. Are you sure a 60GB SSD wil be large enough for your needs?