Contact the computer vendor, they can send you a copy of the restore disks. You can try to do a web search for a .iso copy of the Vista disk, but you need to get the right OEM version for your PC brand. Then make the disk yourself and if you need to re-install, use the Vista code on the computer.
This issue can come up when a hard-drive is failing though, run a full disk scan using either a BIOS option to check the drive, or check the PC vendor's support site for a utility program you can use to scan the hard-drive. If the drive comes up as bad, get a new one.