How to fix a broken registry key if Windows XP is not booting

Recently I modified the Windows XP registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage\OEMCP from 437 to 65001, which resulted an immediate Windows XP system crash, and Windows didn't boot anymore, not even in safe mode. This post describes how I changed the key back without a working Windows on the machine.

• I downloaded SystemRescueCD 1.1.7 from http://www.sysresccd.org/Download, burnt it to CD, booted the system from it.
  
• I pressed Enter at the CD boot menu to boot with the default options.
  
• I waited a few minutes for the SystemRescueCD Gentoo system to boot.
  
• At the root@sysresccd /root % prompt (I pressed Alt-F2 at the help screen), I listed the partitions with the command fdisk -l. It turned out that my Windows XP partition was /dev/sda1.
  
• I created a mount point directory with mkdir /mnt/, and mounted the Windows XP partition with mount -t ntfs-3g /dev/sda1 /mnt/p .
  
• I edited the system registry with chntpw -e /mnt/p/WINDOWS/system32/config/system (see the transcript below).
  
• I ensured that changes are written to disk sync.
  
• I rebooted without the CD, and now my Windows XP worked.

Here is the transcript of the chntpw session:

chntpw version 0.99.5 070923 (decade), (c) Petter N Hagen
Hive  name (from header): 
ROOT KEY at offset: 0x001020 * Subkey indexing type is: 686c <lh>
Page at 0x54c000 is not 'hbin', assuming file contains garbage at end
File size 5767168 [580000] bytes, containing 1301 pages (+ 1 headerpage)
Used for data: 103727/5482832 blocks/bytes, unused: 2263/25616 blocks/bytes.

Simple registry editor. ? for help.

> ls
Node has 7 subkeys and 0 values
  key name
  <ControlSet001>
  <ControlSet002>
  <LastKnownGoodRecovery>
  <MountedDevices>
  <Select>
  <Setup>
  <WPA>

> cd \ControlSet001\Control\Nls\CodePage

\ControlSet001\Control\Nls\CodePage> cat OEMCP

Value <OEMCP> of type REG_SZ, data length 12 [0xc]
65001


\ControlSet001\Control\Nls\CodePage> ed OEMCP
EDIT: <OEMCP> of type REG_SZ with length 12 [0xc]
[ 0]: 65001

Now enter new strings, one by one.
Enter nothing to keep old.
[ 0]: 65001
-> 437
newkv->len: 8

\ControlSet001\Control\Nls\CodePage> q

Hives that have changed:
 #  Name
 0  <system>
Write hive files? (y/n) [n] : y
 0  <system> - OK

Please note that a similar procedure (with the exact same fdisk, mount, and chntpw comamnds) using the Knoppix 5.3.1 live CD instead of SystemRescueCD.

Please note that it is possible to edit any registry file with the Windows XP regedit. Here are some relevant links how to do this: http://smallvoid.com/article/winnt-offline-registry-edit.html; http://www.hardforum.com/showthread.php?t=1162302; http://www.911cd.net/forums//index.php?showtopic=7066.

Please note that it is possible to edit the registry with the regedit application shipping with the ERD Commander 2005 Windows XP live boot CD. Get the CD from http://www.fullandfree.info/software/erd-commander-2005/ . There is a Linux tool nrg2iso which can convert the .nrg file in the download for burning to CD. On Windows, it is possible to burn the .nrg file using ImgBurn.

Here are some methods which I tried, but they didn't work to edit the registry system registry file:

• Using kregedit – it crashed opening the system registry file.
  
• Running wine's /usr/bin/regedit – I wasn't able to specify which file to edit.
  
• Running wine regedit.exe with the Windows XP regedit.exe – it failed to start up because it hasn't found some DLLs. I haven't bothered forcing it.