How do I remove an extra operating system from by

If you just formatted the partition with the second XP installation on there, it should remove the boot menu where you choose which installation to go to.
Here are a few options for you to choose from.

• Option One: Open Start-Run and enter msconfig Click the tab "BOOT.INI" The contents of the boot.ini file are shown and a number of configuration settings are available. Under Operating systems, delete the one you don't want. Be careful not to delete the wrong one.
• Option Two: Right-click on "My Computer" and choose "Properties" from the context menu. The System Properties dialog box will open. In the section "Startup and Recovery" click the button "Settings". To delete the unwanted operating system from the boot display menu, use the "Edit" button on the right of the entry.
  
• Option Three: If the OS is Windows XP Professional, it has a command line utility for manipulating boot.ini called bootcfg.exe.
  Click start, type CMD, click OK and you are presented with the command prompt. Type bootcfg /? It will list the description and parameter list. Once again, you can delete the unwanted OS.
• Option Four: Boot to the XP install disk and open up the command prompt utility of the disk. Enter "fixmbr" and press enter. Restart the computer and remove the disk.
  

Issue:NTOSKRNL.EXE is missing or corrupt.
Related errors:
Below is a listing of the full error message that may be related to this error.
Windows NT could not start because the below file is missing or corrupt:
C:\Winnt\System32\Ntoskrnl.exe
Cause:

1. Keyboard issue
2. Miscellaneous corruption
3. Corrupt boot.ini file.
4. Missing boot.ini file.
5. Missing or corrupt ntoskrnl.exe file.
6. Windows NT installed on a partition bigger then 7.8GB
7. Corrupted hard disk drive or severely corrupted Windows.

Solution:Keyboard issue
This issue has also been known to be caused by a short in the ground wire in the keyboard cable. Make sure this is not the cause of your error by replacing the keyboard with a different keyboard or simply just disconnecting the keyboard from the computer.
Miscellaneous corruption
Before trying any of the below recommendations it's recommend that you attempt to load the last known good configuration. Additional information about doing this can be found on document CH000626.
Corrupt boot.ini file
This issue is often caused when the boot.ini is missing or improperly configured. This issue often arises after a user has recently added or removed an operating system on the computer or added or removed hard disk drives in the computer.
Make sure the line pointing to the operating system and its drive and partition is properly configured in the [boot loader] and [operating systems] section. Additional information about boot.ini can be found on document CH000492.
Missing boot.ini file
Microsoft Windows XP users:
If the boot.ini is severely corrupted or missing a user running Microsoft Windows XP can rebuild the boot.ini to resolve this issue. Additional information about rebuilding the boot.ini can be found on document CH000648.
Microsoft Windows NT and Windows 2000 users:
To restore the original boot.ini file in Microsoft Windows NT or Windows 2000 you will need an ERD and follow the below steps. If you do not have an ERD you will be unable to follow these steps.

1. Boot the computer with your Windows NT three setup diskettes or the Windows 2000 setup disc.
2. In the setup menu, type R to start the repair.
3. When prompted for the ERD diskette insert the diskette and inspect the startup environment.

Missing or corrupt ntoskrnl.exe file
If the ntoskrnl.exe file is corrupt or missing this can also generate the error. To restore this file follow the below steps.

1. Insert the Microsoft Windows XP CD. Note: If you have a recovery CD or a restore CD and not a Microsoft Windows XP CD it is likely the below steps will not resolve your issue.
2. Reboot the computer, as the computer is starting you should see a message to press any key to boot from the CD. When you see this message press any key.
3. In the Microsoft Windows XP setup menu press the R key to enter the recovery console.
4. Select the operating system you wish to fix, and then enter the administrator password.
5. Type expand d:\i386\ntoskrnl.ex_ c:\windows\system32
6. You will then be prompted if you wish to overwrite the file type Y and press enter to overwrite the file.
7. Type exit to reboot the computer.

Windows NT installed on a partition bigger then 7.8GB
If you are running Microsoft windows NT 4.0 on a partition larger than 7.8GB this issue can occur if the boot files are located outside this limitation. When this error occurs your computer will have the error message as shown below.
OS Loader v4.01
Disk I/O error status=00000001
Windows NT could not start because the below file is missing or corrupt: winnt\system32\Ntoskrnl.exe
Please reinstall a copy of the above file.
If your system partition is larger than 7.8GB you will need to delete the partition and recreate the partition to 7.8GB or less. Additional information about this issue can be found on Microsoft KB Q224526.
Corrupted hard disk drive or severely corrupted Windows
Attempt to check the hard disk drive for any errors by running the chkdsk program. To do this follow the below steps.

1. Insert the Microsoft Windows XP CD. Note: If you have a recovery CD or a restore CD and not a Microsoft Windows XP CD it is likely the below steps will not resolve your issue.
2. Reboot the computer, as the computer is starting you should see a message to press any key to boot from the CD. When you see this message press any key.
3. In the Microsoft Windows XP setup menu press the R key to enter the recovery console.
4. Select the operating system you wish to fix, and then enter the administrator password.
5. Once at the recovery console type chkdsk /r
6. Once completed type exit and see if issue is resolved.

If after trying all of the above steps you are still encountering the same issue it's likely that Windows is severely corrupted and it is recommended you attempt to reinstall Windows. Additional information about erasing the computer and starting over can be found on document CH000186.
Finally, if during the Windows installation you encounter errors it's likely that your hard disk drive is bad.

The Boot Configuration Data (BCD) store contains boot configuration parameters and controls how the operating system is started in Microsoft®Windows Vista.
Remove Windows Vista From Dual Boot System Windows Vista works slightly different from earlier versions of Windows when installed on a dual boot system, in that it has a completely different boot loader.
When Windows Vista is first installed as a dual boot operating system a new boot folder is added to the root directory of your PC. This is a hidden file and therefore is not noticed. When you boot your PC a menu appears with the following options:

• Earlier versions of Windows
• Windows Vista

Clicking the Windows Vista option will boot the PC into Windows Vista. If, however, you select the earlier versions of Windows option, another menu will appear from which you can choose Windows XP or whatever earlier version - Windows 2000 or Windows 2003 server - you installed first.
Because of this new boot loader it is not as easy to remove Vista from a dual boot system scenario. Simply deleting the Vista partition will, of course, remove Windows Vista, but, unfortunately, it will not remove the Windows Vista boot loader. For this reason, if you simply delete the Windows Vista partition, on rebooting your machine you will not automatically boot into Windows XP (or an earlier version). Instead you will once again be presented with a menu from which you have to choose which operating system you wish to boot to.
Obviously, once you have removed the boot loader and rebooted the Vista operating system will still be on the partition you originally installed it on. To remove Vista completely you will need to Delete the partition that Windows Vista was installed upon.
To remove this menu, or more to the point, the boot loader, proceed as follows:
1/ Boot the PC to Windows Vista
2/ Ensure you are logged onto the Internet and then download the freeware boot loader utility VistaBootPro (www.vistabootpro.org)
3/ Once you have downloaded VistaBootPro, install it on your machine
4/ During Install VistaBootPro will install an icon on your desktop
5/ Locate the VistaBootPro icon and Right Click on it. Then, from the drop down menu, Click on the Run As Administrator option
6/ User Account Control (UAC) will pop up and ask for permission to run the program
7/ After you have given UAC permission - you must be the administrator or have administrator privileges - VistaBootPro will run.
8/ Once VistaBootPro opens, Click on the Bootloader tab
9/ In the Bootloader Maintenance section, Click on the Radio button next to the option marked 'Uninstall the Vista Bootloader (Used to restore Legacy OS) option' and then Click the Apply button
10/ Finally Reboot your PC
11/ On rebooting your machine you will boot directly into Windows XP (or an earlier operating system). No menu will appear.
12/ All that is left to do now is to delete the partition which originally contained Windows Vista. (Assuming you wish to remove the Vista partition from your hard drive).

which operating system are you using?...if it is windows XP, you can do a re-install that will replace the missing files....
you do this by going about the install in the normal way, until you get a few screens in when you be informed that windows has found another version of the operating system, and do you wish to fix that installation...check yes, and proceed....any questions, just ask!!!