This is really useful guide from Microsoft that outlines practical steps you
can take to get an XP system working that is experiencing start-up problems.
What I like about it is that it covers just about every kind of start-up
problem. If you are an XP user I suggest you print out this guide and keep it
handy as sooner or later, you are going to need it.
http://www.techsupportalert.com/content/how-fix-windows-xp-system-wont-start.htm