There are a number of things to try first, before a major configuration rebuild.
Re-installing Windows XP
If you need to reinstall WindowsXP and want to keep all your current installed applications and settings:
Start WindowsXP
Click START
Click RUN
Type in 'CMD [enter]'
then: go to the location of your source files if your CD is in 'E' then
Type in 'E: [enter]'
Type in 'CD I386 [enter]'
Type in 'WINNT32 /unattend [enter]'
This will reinstall Windows without obliterating the registry entries for software and wiping out user files in My Documents Folder etc.
I've often need to do this to repair something that had gotten corrupted and didn't want to do a clean install.
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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
Insert and boot from your WindowsXP CD
At the second R=Repair option, press the R key
This will start the repair
Eventually you will be prompted for your XP key
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NTOSKRNL Missing or Corrupt
If you get an error that NTOSKRNL not found:
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
Change to the drive that has the CD ROM.
CD i386
expand ntkrnlmp.ex_ C:\Windows\System32\ntoskrnl.exe
If WindowsXP is installed in a different location, just make the necessary change to C:\Windows
Take out the CD ROM and type exit
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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
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Corrupted or Missing \WINDOWS\SYSTEM32\CONFIG
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