Vista boot problems (missing operating system) ?
If you attempt a multi-boot of Windows Vista/7 with another Windows/Linux OS, a side effect is that Vista can sometimes become unbootable with a dreaded "Missing Operating System" message.
When this happens, you need to attempt to recover the primary drive Master Boot Record and set the partition active (provided you haven't introduced any new drives).
The first step involves booting from the Vista DVD, and clicking "Repair your computer". Instead of letting Windows attempt an automatic recovery, or if the OS is not listed in the "System Recovery" screen, click "Next" to get to the manual System Recovery Options.
Startup Repair can sometimes work, but more often than not it can't repair the computer automatically.
Enter the recovery environment Command Prompt and try the following commands:
chkdsk /R (to check the filesystem and attempt bad sector recovery)
bootrec /fixboot (to attempt and recover the boot sector)
bootrec /scanos (to see if it finds Vista)
bootrec /rebuildbcd (to try rebuilding the boot manager)
Sometimes bootrec /fixboot tells you "the volume does not contain a recognized file system."
bootrec /rebuildbcd may find Vista, yet can exit with the error: "The volume does not contain a recognized file system" error. In that case, you'd need to use the "diskpart" and set the Windows partition to active. Run bootrec /fixboot and bootrec /rebuildbcd again after setting the partition to active with the diskpart tool.
At this point, Vista should either boot normally, or you can attempt the automatic startup repair from the Vista DVD to get to it.