First thing to do is to check your keyboard, a faulty connection can cause this.
Second. Your boot.ini may be corrupt and may need to be repaired:
1. Insert the Microsoft Windows XP CD.
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. When you reach the command prompt type the following command and then press Enter.
bootcfg /rebuild
The bootcfg utility will scan your hard drives for any Windows XP installations and then display the results. Follow the remaining steps to add your Windows XP installation to the boot.ini file.
6. The first prompt asks Add installation to boot list? (Yes/No/All).
Type Y in response to this question and press Enter.
7. The next prompt asks you to Enter Load Identifier:.
This is the name of the operating system. For example, type Windows XP Professional or Windows XP Home Edition and press Enter.
8. The final prompt asks you to Enter OS Load options:.
Type /Fastdetect here and press Enter.
9. Type exit to reboot the computer.
Thirdly, if the ntskrnl32.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.
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\ntskrnl32.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.
Fourth, as a last resort, restore Windows from a backup or re-install Windows.
