A partir do artigo do TechNet apropriadamente nomeado (e razoavelmente SEO-friendly) " O que é o Sysprep? ":
[...] Sysprep also enables you to prepare an image to be delivered to a customer. When the customer boots Windows, Windows Welcome starts.
Em seguida, segue um aviso geral sobre o uso apropriado:
Sysprep must be used only to configure new installations of Windows. You can run Sysprep as many times as required to build and to configure your installation of Windows. However, you can reset Windows activation only up to three times. You must not use Sysprep to reconfigure an existing installation of Windows that has already been deployed. Use Sysprep only to configure new installations of Windows.
O terceiro parágrafo introdutório até mergulha no porquê:
If you intend to transfer a Windows image to a different computer, you must run sysprep /generalize, even if the computer has the same hardware configuration. The sysprep /generalize command removes unique information from your Windows installation, which enables you to reuse that image on different computers. The next time you boot the Windows image, the specialize configuration pass runs. During this configuration pass, many components have actions that must be processed when you boot a Windows image on a new computer. Any method of moving a Windows image to a new computer, either through imaging, hard disk duplication, or other method, must be prepared with the sysprep /generalize command. Moving or copying a Windows image to a different computer without running sysprep /generalize is not supported.
Desculpe dizer isso, mas ... você não deveria ter feito isso, é hora de restaurar a partir do backup