Repair Install

If XP is corrupted to the point where none of the previous solutions get it to boot,
you can do a Repair Install that might work as well as keep the current settings.
Make sure you have your valid WindowsXP key.
The whole process takes about half an hour depending on your computer
If you are being prompted for the administrator’s password, you need to choose the 2nd repair option, not the first.
Insert and boot from your WindowsXP CD
At the second R=Repair option, press the R key
This will start the repair
Press F8 for I Agree at the Licensing Agreement
Press R when the directory where WindowsXP is installed is shown. Typically this is C:\WINDOWS
It will then check the C: drive and start copying files
It will automatically reboot when needed. Keep the CD in the drive.
You will then see the graphic part of the repair that is like during a normal install of XP (Collecting Information, Dynamic Update, Preparing Installation, Installing Windows, Finalizing Installation)
When prompted, click on the Next button
When prompted, enter your XP key
Normally you will want to keep the same Workgroup or Domain name
The computer will reboot
Then you will have the same screens as a normal XP Install
Activate if you want (usually a good idea)
Register if you want (but not necessary)
Finish
At this point you should be able to log in with any existing accounts.

NTLDR or NTDETECT.COM Not Found

If you get an error that NTLDR is not found during bootup,
If you have FAT32 partitions, it is much simpler than with NTFS.
Just boot with a Win98 floppy and copy the NTLDR or NTDETECT.COM files
from the i386 directory to the root of the C:\ drive.
For NTFS:
Insert and boot from your WindowsXP CD.
At the first R=Repair option, press the R key
Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1
Enter in the administrator password when requested
Enter in the following commands (X: is replaced by the actual drive letter that is assigned to the CD ROM drive.
COPY X:\i386\NTLDR C\:
COPY X:\i386\NTDETECT.COM C:\
Take out the CD ROM and type exit

HAL.DLL Missing or Corrupt

If you get an error regarding a missing or corrupt hal.dll file, it might simply be the BOOT.INI file on the root of the C: drive that is misconfigured
Insert and boot from your WindowsXP CD.
At the first R=Repair option, press the R key
Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1
Type bootcfg /list to show the current entries in the BOOT.INI file
Type bootcfg /rebuild to repair it
Take out the CD ROM and type exit

Corrupted or Missing

If you get the error:
Windows could not start because the following files is missing or corrupt
\WINDOWS\SYSTEM32\CONFIG\SYSTEM or \WINDOWS\SYSTEM32\CONFIG\SOFTWARE
Insert and boot from your WindowsXP CD.
At the first R=Repair option, press the R key
Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1
Enter in the administrator password when requested
cd \windows\system32\config
Depending on which section was corrupted:
ren software software.bad or ren system system.bad
Depending on which section was corrupted
copy \windows\repair\system
copy \windows\repair\software
Take out the CD ROM and type exit