If your OS is WinXP, you can try this
1. Using WinXP Installer CD, Boot from CD and select the first repair option (R) which will take you to the Recovery Console. Now copy the missing/corrupt file from the CD to your hard disk by typing ‘copy D:\i386\ntoskrnl.exe C:\Windows\system32\ntoskrnl.exe’ (remove the quotes) and press Enter.
2. If you can only find ntoskrnl.ex_ on the CD then the file needs to be expanded by typing ‘expand D:\i386\ntoskrnl.ex_ C:\Windows\system32\ntoskrnl.exe’ (quotes not included) and press Enter.
If 1 and 2 above do not work, rename the file by typing ‘ren C:\Windows\system32\ntoskrnl.exe C:\Windows\system32\ntoskrnl.old’ (remove quotes) and press Enter. Then try again.
3. If it’s still not working, type chkdsk /r (note the space) and press Enter.
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