(updated 12/16/2012)

Corrupt registry keeps Windows XP from starting in any mode...

If a computer with Windows XP installed will not get past the loading of the operating system and continually cycles, restarting itself, no matter what choice is made in the startup options (i.e. Safe Mode, Normal, Last Known Good, etc.), the registry may be corrupt - and for no good reason.

PCs that have been running successfully for days and months without problems can suddenly have this problem, causing those trying to repair them to look at all the "usual suspects" first, (video cards, sound cards, network cards, card settings, BIOS settings, hardware drivers) only to be forced to reinstall the operating system as a final solution.

Here is something to try as an alternative...

Microsoft Knowledge Base Article - 307545

How to Recover from a Corrupted Registry That Prevents Windows XP from Starting

"This article describes how to recover a Windows XP system that does not start because of corruption in the registry. This procedure does not guarantee full recovery of the system to a previous state; however, you should be able to recover data when you use this procedure."

Case study...

A PC with Windows XP installed would not boot fully to the desktop no matter which startup option was used. It would reach a certain point (in Safe Mode, it would show mup.sys as the last component installed, then would never get past installing whatever comes next, or in Normal Mode, it would briefly show a blue-screen error) then keep cycling continuously in warm boots. Disabling any and all hardware as a debugging technique had no effect. Removing and replacing any and all hardware had no effect.

Using information from the Microsoft article noted above, key files from an earlier time were recovered and then used to overwrite the existing corrupt files causing the problem. The hard drive of the troubled PC was removed and placed in a good PC to expedite the fix.

The files were... system software sam security default

...in the c:\windows\system32\config folder. (They do not have extensions.)

The replacement files came from the System Volume Information folder. This folder does not readily appear, as it is set as a super-hidden folder. This folder will contain one or more _restore {GUID} folders such as "_restore{87BD3667-3246-476B-923F-F86E30B3E7F8}".

Note : if you receive the error message "C:\System Volume Information is not accessible. Access is denied.", see the Microsoft Knowledge Base article 309531 to gain access to this folder and continue with the procedure. Also, see image below...

The path looks like this : c:\system volume information\_restore{D86480E3-73EF-47BC-A0EB-A81BE6EE3ED8}\RP1\snapshot

If you have a choice, right-click on the folders to find one that goes back to a previous time when the troubled PC was running correctly. From its Snapshot folder, copy the five files (system software sam security default) to the c:\windows\system32\config folder, overwriting the existing corrupt ones.

In the case study, after this was done and the hard drive was returned to its place, the PC booted correctly and was restored.

The Microsoft article has a fuller and safer technique that can be performed on a troubled PC without taking its hard drive out, so you may prefer to follow its longer instructions.

The image below refers to the "take ownership" condition noted above...

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