"You can attempt to repair this file by starting windows setup using the original setup CD-Rom. Select "r" at the first screen to start repair. Do NOT use an OEM "Recovery Disc". Only a valid Windows XP media will work or a disc from the OEM that says "Operating System" may sometimes work depending on how the manufacturer labeled the CD.
Recovery Console
The Windows XP Recovery Console1.
The Recovery Console is a command line console (you know, MS-DOS like window) that allows you some access to your computer (basically, your crashed computer...sorta like Windows 98 boot to command prompt only). It's not full of features but when you're in a jam it does a great job. It's not necessary to pre-install the Recovery Console but it does help.
To enter into the Recovery Console you have two options:
1.) Reboot the computer and before the Windows Logo screen appears tap F8. If you're lucky, you'll have the option to boot into Recovery Console.
2.) If you're not lucky enough to have the option to boot into Recovery Console via step one, find your Windows XP CD and boot from it. Once it loads the files it'll ask what you want to do. You're going to select the "R" option to repair the pc via Recovery Console.
Once you get into the Recovery Console it'll ask which Windows install you want to use. If you're a regular computer user there should only be 1 listed (Usually listed as 1. C:\windows ) if you're a more "advanced" user there might be more listed. It is assumed you should then know which one to boot into if you know how to setup a multi-boot system.
After selecting the Windows installation you would like to boot by pressing the respective number you will be asked for the Administrator's password. It's time to enter it.
Please note:
There is a built-in “Administrator” account when you install Windows 2000 or Windows XP. When entering the recovery console that is the password the recovery console is asking for. It is not asking for the account you created during install or the one that you generally login to. Unless, of course, you're logging into the built-in administrator's account which is not a good idea. If the password was/is blank then you shouldn't get a prompt asking for a password. It'll just load into a C:\> prompt. However, if it asks for a password and you don't remember setting one then there is a known issue with OEM versions of Windows XP and Sysprep (don't worry about sysprep, for another time) with administrator's passwords. If that's the case, then just visit this http://support.microsoft.com/kb/308402/en-us website to download and use updated Windows XP Setup Floppies for your version of Windows XP. If by chance you have forgotten the password, I'm sorry, we can't help you recover it. You can, however, read option 3 or 4 for a way to repair your computer.
Option 1
Firstly, it is in my belief that since you're having issues loading a file (the windows registry is a database of files, so yes, it's a file issue) that you could also be having an issue with your hard drive. I also believe that since that that your drive could be going bad it is best to determine if that is the case or not first. The reason behind that is because the more you read/write from the bad drive, the more of a possibility you have of losing important information by causing more irreversible damage to the drive by reading and writing to/from the drive.
What I recommend to do first is to read an article by steamwiz on how to backup your files from an unbootable computer. That article is located at http://www.help2go.com/Tutorials/Computer_Basics/How_to_recover_files_from_an_unbootable%10dead_computer.html. Tip, in the article, steamwiz mentions a linux live cd named Knoppix. If you follow the article and download Knoppix please make sure to download knoppix version 5.0 or higher, it may help you later in this tutorial. After backing up your files, find out your hard drive manufacturer by opening the side of the case. All you have to do is look at the drive label and find out who makes it. More often than not you will not have to unplug anything to view the label of your drive so don't worry about that. Once you figure out who the manufacturer of your drive is go here to learn about their drive diagnostic utilities: http://www.tacktech.com/display.cfm?ttid=287
Note:
I urge you to read all documentation supplied with your hard drive manufacturer's drive diagnostics. The reason, if you go through the menus and pick the wrong option you can inadvertently erase the contents of your entire drive. I'm not trying to scare you from doing a drive diagnostic, just making sure you are warned about not reading the documentation.
If your drive came back OK after running the drive diagnostic utilities then continue. If your drive came back bad or you encountered an error during the diagnostics please call a tech support company in your area or post to our forums.