boot - Removing or disabling software that prevents Windows from booting

A piece of software I installed recently has gone mad, and I can no longer boot Windows. How can I remove that application, or at least prevent it from running at startup? Neither Safe Mode nor Safe Mode with Command Prompt work. Is there anything I can do short of reinstalling Windows?

Answer

I don't know which Windows you are using. At least for Windows XP, you can make something like a Bart PE bootable CD, (Windows PE stands for Windows Preinstallation Environment), boot from the CD, load the registry hive (you will probably need the file named "system") using the Registry Editor from the boot CD, and remove the autorun entries manually. The registry hives are stored at C:\Windows\System32\Config\ (Source). There is a guide with graphics illustrations here.

The autorun programs are usually stored in these places:

The Registry keys most often involved
with startup have the word "Run" in
them somewhere. They are listed below
using the abbreviation HKLM for the
major key (or "hive") called
"HKEY_LOCAL_MACHINE" and HKCU for for
the hive "HKEY_CURRENT_USER"

• HKLM\Software\Microsoft\Windows\CurrentVersion\Run


• HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce


• HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices


• HKLM\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce


• HKCU\Software\Microsoft\Windows\CurrentVersion\Run


• HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce


• HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnceEx

I don't know if this method will work with Windows Vista or Windows 7 installations; I have never tried to find it. But it definitely works with XP.

Another option is to use a registry tool in Hiren's BootCD, like

Registry Editor PE 0.9c - Easy editing of remote registry hives and user profiles.