Lifted from above site:
If the Last Known Good Configuration option fails try the Recovery Console.
An easy to follow recovery console description when unable to start computer due to corrupt registry.
Click on Tutorial then the Charlie White article on XP crash.
This is a laymans version of Q307545 in simple language.
If they don't work you could try repairing windows itself by running it over itself. You will lose all your windows updates but your files will be untouched.
How to Perform an In-Place Upgrade (Reinstallation) of Windows XP (Q315341)