Hi
Use a live cd such as bartpe ot UBCD, then boot on this cd.
http://community.plus.net/blog/2008/...-the-easy-way/
or
http://www.the-pc-guru.com/How_to_re..._registry_.php
To carry out the steps described below you must have access to a Microsoft Windows XP installation CD, which you can boot from to access the Recovery Console.
If you don't have a Windows XP CD, you can carry out the same steps using a different boot CD such as Bart's Preinstalled Environment (BartPE) bootable live windows CD/DVD. The same principles, if not the same commands, could also be applied when using a Linux-based recovery disc such as the Ultimate Boot CD.
•Check the boot priority in the Bios settings to ensure the computer will boot from CD-Rom.
•Boot from your Windows XP CD.
•Start Windows Setup.
•Press R to access the recovery console.
•Select your Windows installation.
•Type the administrator password (just press enter if you don't have one.)
•Enter the following commands:
CD C:\
CD “system volume information\_resto~1”
DIR
•Pick the restore point (RPx) you wish to use, using the folder date stamps to guide you.
•Enter the commands:
CD RPx (x is the restore point you chose)
CD SNAPSHOT
•Copy the registry backups so that they overwrite the existing registry files:
COPY _registry_machine_system C:\Windows\System32\Config\System
COPY _registry_machine_software C:\Windows\System32\Config\Software
COPY _registry_machine_sam C:\Windows\System32\Config\Sam
COPY _registry_machine_security C:\Windows\System32\Config\Security
COPY _registry_user_.default C:\Windows\System32\Config\Default
•Type the command exit to close the Recovery Console and restart the computer.
Use Last Known Good Configuration
To use the Last Known Good Configuration feature, first restart the computer by pressing [Ctrl][Alt][Delete]. When you see the message Please select the operating system to start or hear the single beep, press [F8] to display the Windows Advanced Options menu. Select the Last Known Good Configuration item from the menu and press [Enter].
Keep in mind that you get only one shot with the Last Known Good Configuration feature. In other words, if it fails to revive your Windows XP on the first attempt, the backup copy is also corrupt.
Fix a corrupt master boot record
If you suspect Windows XP won't boot because the master boot record has been corrupted, you can use the Recovery Console tool Fixmbr to fix it. First, boot the system with the Windows XP CD and access the Recovery Console as described in #4.
To use the Fixmbr tool, from the Recovery Console command prompt, type
Fixmbr [device_name]
Where [device_name] is the device pathname of the drive to which you want to write a new master boot record. For example, the device pathname format for a standard bootable drive C configuration
To create a Windows startup disk, insert a floppy disk into the drive of a similarly configured, working Windows XP system, launch My Computer, right-click the floppy disk icon, and select the Format command from the context menu. When you see the Format dialog box, leave all the default settings as they are and click the Start button. Once the format operation is complete, close the Format dialog box to return to My Computer, double-click the drive C icon to access the root directory, and copy the following three files to the floppy disk:
Boot.ini
NTLDR
Ntdetect.com
After you create the Windows startup disk, insert it into the floppy drive on the afflicted system and press [Ctrl][Alt][Delete] to reboot the computer. When you boot from the Windows startup disk, the computer will bypass the active partition and boot files on the hard disk and attempt to start Windows XP normally.
OR
Try resetting CMOS. Many times the problem is that simple to fix once you find the correct jumper. Before you start make sure your computer is unplugged and the power supply is switched off. Frequently, the reset CMOS jumper is labeled as, “jp1”, “reset cmos” and “JBAT1”. If you can not tell which jumper it is, consult your motherboard manual. Simply move the shunt (little removable piece) off pins 1-2 and move it to pins 2-3. By placing the shunt on pins 2-3 you are completing a circuit. This circuit erases all the settings you changed in CMOS and sets them back to factory defaults. Leave the pins shorted for about 10 seconds to be safe. Another method of resetting CMOS is removing the motherboard battery and then putting it back a few seconds later. The battery is a little metal circular object, simply pull back the tab and pop it out. Frequently, the reset CMOS jumper is near or next to the battery. Sometimes changing a setting improperly can cause a computer not to boot up, so if that’s the problem this remedy should cure it. Make sure that when you try to turn your computer back on that the jumper is not still set to Clear CMOS
http://www.aitechsolutions.net/winxpnoboot.html