Hopefully, you made a backup of your VHB system before starting the upgrade.
If so, just restore from the backup.
If you did not make a backup and Vista Home Basic came preinstalled on your
computer then use the Restore software that came with the computer. If you
did not get recovery dvds then the recovery software should be in a hidden
partition on the computer. Generally you press a function key when starting
up to restore the computer to factory condition. On my laptop it is the F11
key. You did not say what make and model computer you have, so no one can
really say what you should do.