After you install Windows Vista Service Pack 1 (SP1), existing system restore points may no longer be available. Additionally, shadow copies of files may have been removed as part of the service pack installation.
Note To view the shadow copies of a file, right-click the file, click Properties, and then click the Previous Versions tab
This issue occurs when you install Service Pack 1 (SP1) for Windows Vista on a computer that is low on available disk space. When you try to install the service pack on a computer that is low on available disk space, the installation process frees disk space by removing any existing system restore points and by creating a single new system restore point
To work around this issue, free additional disk space before you try to install Vista SP1. The more free space that is available when you install the service pack, the less likely it is that existing restore points and shadow copies of files will be deleted.
For more information about how to free disk space in Windows Vista, see Windows Vista Help and Support. To see Windows Vista Help and Support, follow these steps
Click Start, and then click Help and Support.
In the Search Help box, type disk cleanup, and then press ENTER.