I have a sony vaio pcg-7a2l notebook It has the following error message windowsroot>\system32\ntoskrnl.exe missing or corrupt. It won't boot, I tried booting from cdrom in order to repair the OS. I change the boot order in the bios to optical drive. No success! Need help any would be apreciated.

Try this "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. 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. 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. In the Microsoft Windows XP setup menu press the R key to enter the recovery console. Select the operating system you wish to fix, and then enter the administrator password. Type expand d:\i386\ntoskrnl.ex_ c:\windows\system32 You will then be prompted if you wish to overwrite the file type Y and press enter to overwrite the file. Type exit to reboot the computer. "