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There is performed a backup of the system configuration, after each successful login. This name of this backup is Last Known Good Configuration (LKGC). It is possible to make use of the LKGC during the startup of Windows (Press F8). This enables one to recover from different situations where Windows cannot boot:

• Installed faulty driver
• Disabled critical driver
• Disabled critical service

The LKGC resides in the following registry file (Along with the active configuration):

%systemroot%\System32\Config\System

Note if this file becomes corrupted, then it means that both the active configuration and LKGC becomes corrupted.

The LKGC can be seen using the registry editor:

[HKEY_LOCAL_MACHINE \SYSTEM \ControlSetXXX]  (Ex. ControlSet002)

[HKEY_LOCAL_MACHINE \SYSTEM \Select]
LastKnownGood = XXX

More Info MS KB Q100010
More Info MS KB Q142033

Note it is possible to configure whether the LKGC should be created after every login:

[HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \Windows NT \CurrentVersion \Winlogon]
ReportBootOk = 1 (Enabled = 1, Disabled = 0, Default = No Value; Enabled)

More Info MS KB Q136441

Note to make best use of LKGC, then after making a "critical" change and restarted, then don't login right away (Or Automatic Login). Instead wait about a minute after the login screen has shown itself, so that services etc. can load completely and if no errors occurs then login.

More Info MS KB Q101790
More Info MS KB Q307852