All you need is Recovery Console and Safe Mode
You are going to copy the missing and corrupted files from an OS disc.
Do this:
A-1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.
Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted to do so.
2. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3. If you have a dual-boot or multiple-boot computer, select the installation that you want to access from the Recovery Console.
4. When you are prompted to do so, type the Administrator password. If the administrator password is blank, just press ENTER.
5. At the Recovery Console command prompt, type the following lines, pressing ENTER after you type each line:
md tmp
copy c:\windows\system32\config\system c:\windows\tmp\system.bak
copy c:\windows\system32\config\software c:\windows\tmp\software.bak
copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
copy c:\windows\system32\config\security c:\windows\tmp\security.bak
copy c:\windows\system32\config\default c:\windows\tmp\default.bak
delete c:\windows\system32\config\system
delete c:\windows\system32\config\software
delete c:\windows\system32\config\sam
delete c:\windows\system32\config\security
delete c:\windows\system32\config\default
copy c:\windows\repair\system c:\windows\system32\config\system
copy c:\windows\repair\software c:\windows\system32\config\software
copy c:\windows\repair\sam c:\windows\system32\config\sam
copy c:\windows\repair\security c:\windows\system32\config\security
copy c:\windows\repair\default c:\windows\system32\config\default
6. Type exit to quit Recovery Console. Your computer will restart.
B-1. Click Start, click Shut Down (or click Turn Off Computer), click Restart, and then click OK (or click Restart).
2. Press the F8 key.
3. Use the arrow keys to select the appropriate Safe mode option, and then press ENTER.
4. If you have a dual-boot or multiple-boot system, use the arrow keys to select the installation that you want to access, and then press ENTER.
In step B, you are going to copy the registry files from their backed up location by using System Restore. This folder is not available in Recovery Console and is generally not visible during typical usage. Before you start this procedure, you must change several settings to make the folder visible:
This is for preventing the damage of the system32.
C-1. Start Windows Explorer.
2. On the Tools menu, click Folder options.
3. Click the View tab.
4. Under Hidden files and folders, click to select Show hidden files and folders, and then click to clear the Hide protected operating system files (Recommended) check box.
5. Click Yes when the dialog box that confirms that you want to display these files appears.
6. Double-click the drive where you installed Windows XP to display a list of the folders. If is important to click the correct drive.
7. Open the System Volume Information folder. This folder is unavailable and appears dimmed because it is set as a super-hidden folder.
Any yeah how would the HDD be damaged by light as im assuming no-one is taking the drive out, then taking it apart, and even if it was that it wouldn't just corrupt the odd reg entry!
This fix worked perfectly!!!
Try this one first before the windows fix!!
Windows one did not work for me but this one was flawless!!!!!!!!!!!!!!!!!!!!!!!!!!!!!11