go to command and write bootcfg
if it shows windowsvista and windows xp then there is a way to repair it
else u need to install windows vista again...also try this..might can help u
To use the bootcfg command, start the Recovery Console with the Windows XP CD-ROM, and then click Recovery Console. Or, install the Recovery Console locally, and then select the command from the Boot menu.
The bootcfg command has the following uses:
• The bootcfg /default command sets the default operating system option in the Boot menu. The command selects the operating system entry automatically.
• The bootcfg /add command scans the computer for Windows NT 4.0, Windows 2000, or Windows XP (if it is dual booting) installations, and then displays the results. From this location, you can add an installation to the Boot menu.
You may receive a message that is similar to the following message:
Scanning all disks for Windows Installations
Please wait, since this may take a while...
Total Identified Windows Installs: 2
[1] C:\Windows
[2] D:\Windows
Select installation to add: (select a number)
Enter Load Identifier: (Custom description for an operating system loading from the Boot menu)
Enter Operating System Load Options: (that is: /fastdetect)
This process adds a new entry in the Boot menu. When you add an installation, the bootcfg command also makes the installation the default operating system boot entry.
• The bootcfg /rebuild command scans the hard disks of the computer for Windows NT 4.0, Windows 2000, or Windows XP installations, and then displays the results. You can add the detected Windows installations.
You may receive a message that is similar to the following message:
Total Identified Windows Installs: 2
[1] C:\Windows
Add installation to boot list? (Yes/No/All):
Enter Load Identifier: (Custom description for an operating system loading from the Boot menu)
Enter Operating System Load Options: (that is: /fastdetect)
[2] D:\Windows
Add installation to boot list? (Yes/No/All):
Enter Load Identifier: (Custom description for an operating system loading from the Boot menu)
Enter Operating System Load Options: (that is: /fastdetect)
• The bootcfg /scan command scans the hard disks of the computer for Windows NT 4.0, Windows 2000 or Windows XP installations, and then displays the results.
You may receive a message that is similar to the following message:
Scanning all disks for Windows Installations
Please wait, since this may take a while...
Total Identified Windows Installs: 2
[1] C:\Windows
[2] D:\Windows
• The bootcfg /list command reads the Boot.ini file, and then displays the operating system identifier, the operating system load options, and the operating system location (path).
You may receive a message that is similar to the following message:
Total entries in boot list: 2
[1] Microsoft Windows Whistler Professional
Operating System Load Options: /fastdetect
Operating System Location: D:\Windows
[2] Microsoft Windows Whistler Server
Operating System Load Options: /fastdetect
Operating System Location: C:\Windows
• The bootcfg /redirect command enables redirection in the boot loader with the configuration specified as port and baudrate. This command is used to turn on the Headless Administration feature.
The following example uses this command:
bootcfg /redirect com1 115200
bootcfg /redirect useBiosSettings
• The bootcfg /disableredirect command disables redirection in the boot loader with the configuration specified as port and baudrate. This command is used to turn off the Headless Administration feature.
check it here for more
*support.microsoft.com/kb/291980/