I am curretly using a Lenovo S10. My Pc cannot boot. The error message found was Operating System not found. 1. Where do i get the Microsoft XP Product Code as the sticker at the back of the PC cannot be read any longer? 2. How do I install back the one key recovery if it is a new formatted hard 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.