Hard shutdowns (not shutting down Windows properly) whether intended or occurring unintentionally...are a major contributor to file corruption.
When I have such, the first thing I do is run chkdsk /r (or equivalent from My Computer/Properties) to do what I can to restore the proper order to system files.
Using Chkdsk to Detect File and Folder Corruption - http://searchwincomputing.techtarget.com/t...1263963,00.html
XP Chkdsk, Using the Graphical Version (My Computer) - http://www.updatexp.com/windows-xp-chkdsk.html
The second thing I might suggest is running sfc /scannow. This will replace any damaged or missing system files.
LEARN how to use SFC.EXE (system file checker) in this article! - http://www.updatexp.com/scannow-sfc.html
If the boot problem persisted, I would probably run the fixmbr and/or the fixboot commands from the Recovery Console.
XP RepairUsing FIXMBR Command - http://www.tech-recipes.com/windows_instal...on_tips483.html
If you don't use a password, just hit ENTER when that prompt comes up in the Recovery Console and that will take you to the line where you type fixmbr.