Malware

Method 1.

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.

1.Insert and boot from your WindowsXP CD

2.At the second R=Repair option, press the R key

3.This will start the repair

4.Press F8 for I Agree at the Licensing Agreement

5.Press R when the directory where WindowsXP is installed is shown. Typically this is C:\WINDOWS

6.It will then check the C: drive and start copying files

7.It will automatically reboot when needed. Keep the CD in the drive.

8.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)

9.When prompted, click on the Next button

10.When prompted, enter your XP key

11.Normally you will want to keep the same Workgroup or Domain name

12.The computer will reboot

13.Then you will have the same screens as a normal XP Install

14.Activate if you want (usually a good idea)

15.Register if you want (but not necessary)

16.Finish

17.At this point you should be able to log in with any existing accounts.
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Method 2.

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

1.Insert and boot from your WindowsXP CD.

2.At the first R=Repair option, press the R key

3.Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1

4.Type bootcfg /list to show the current entries in the BOOT.INI file

5.Type bootcfg /rebuild to repair it

6.Take out the CD ROM and type exit
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Method 3.

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

1.Insert and boot from your WindowsXP CD.

2.At the first R=Repair option, press the R key

3.Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1

4.Enter in the administrator password when requested

5.cd \windows\system32\config

6.Depending on which section was corrupted:
ren software software.bad or ren system system.bad

7.Depending on which section was corrupted
copy \windows\repair\system
copy \windows\repair\software

8.Take out the CD ROM and type exit

Please post back if you have any more problems or questions.

Install it and run the registry cleaning part of it (not run on default).

If the error still appears;
Open regedit and search for that entry. Be very careful when you edit the reg key that contains it. Export a backup of the key first.