How to Perform a Windows XP Repair Install

It is extremely important that you backup important data that is not available from other media sources. This backup should be located on a separate hard drive, CD, DVD, network storage, etc. that will not be affected by the repair install. 
Please check out the warning links before attempting the Repair Install. It is to your advantage you follow the suggestions to prevent data loss and especially if you also have the capability to boot into XP, perform the steps listed in the Warning #1 , before proceeding with the repair install.
After completing [if Windows is still accessible] the steps listed to prevent data loss in warning #1 and you did not remedy the no boot situation, you can use an OEM XP Pro or Home, "retail" XP Home or Pro full or upgrade version CD of the same version Home or Pro to perform a Repair Install.  OEM Restore disks or hidden restore folders on the hard drive will not work for the Repair Install. A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied.
A Repair Install will replace files altered by adware and malware, but will not fix an adware, malware problem.
You can use the In place upgrade option to change a Product Key in the event you entered a key that was already activated. The In Place Upgrade also produces the same result as the Repair Install.
Alternate options to Change XP Product Key #18 on the FAQ list.
Setup cannot continue because the version of Windows on your computer is newer than the version on the CD.
If you get a "Setup cannot continue because the version of Windows on your computer is newer than the version on the CD." message, if you continue, you will need to apply the SP 2 updates after the repair install completes, plus you will need to take the following steps to keep your system from being immediately infected with a virus.
1. If you connect directly to the internet without a router or hardware firewall, disconnect from the internet by physically removing the connections cable, removing a wireless card, or any other means of internet connection.
2. After the Repair install is completed, enable the XP firewall or install third party firewall software or router before connecting to the internet.
If you get the "Setup cannot continue because the version of Windows on your computer is newer than the version on the CD.". You should create a slipstreamed copy of your XP CD by using the software and step by steps supplied in the links below.
Slipstream XP
Automatic Updates
If you cannot download Automatic updates after the Repair install , follow the steps in the link below submitted by MS-MVP's Richard Harper and Ron Martell.
Automatic Updates stops working after a repair install of Windows XP

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XP Repair install
Please read carefully and make sure you followed the warning links before initiating the Repair Install. You can print a text version for reference. repair.txt

1. Boot the computer using the XP CD. You may need to change the boot order in the system BIOS so the CD boots before the hard drive. Check your system documentation for steps to access the BIOS and change the boot order.
2. When you see the "Welcome To Setup" screen, you will see the options below   This portion of the Setup program prepares Microsoft
      Windows XP to run on your computer:
   
      To setup Windows XP now, press ENTER.
   
      To repair a Windows XP installation using Recovery Console, press R.
   
      To quit Setup without installing Windows XP, press F3.
   
3. Press Enter to start the Windows Setup.
    
   do not choose "To repair a Windows XP installation using the Recovery Console, press  R", (you Do Not want to load Recovery Console). I repeat, do not choose "To repair a Windows XP installation using the Recovery Console, press  R". 
4. Accept the License Agreement and Windows will search for existing Windows installations.
5. Select the XP installation you want to repair from the list and press R to start the repair. If Repair is not one of the options, END setup. After the reboot read  Warning#2!
6. Setup will copy the necessary files to the hard drive and reboot.  Do not press any key to boot from CD when the message appears. Setup will continue as if it were doing a clean install, but your applications and settings will remain intact.  If you get files not found during the copying stage.
   Blaster worm warning: Do not immediately activate over the internet when asked, enable the XP firewall before connecting to the internet. You can activate after the firewall is enabled. Control Panel - Network Connections.  Right click the connection you use, Properties and there is a check box on the Advanced page.
   KB 833330u Blaster removal
   What You Should Know About the Sasser Worm and Its Variants
   Microsoft Security Bulletin MS04-011
   
7. Reapply updates or service packs applied since initial Windows XP installation. Please note that a Repair Install using an Original pre service pack 1 or 2 XP CD used as the install media will remove SP1/SP2 respectively and service packs plus updates issued after the service packs will need to be reapplied.