Have you ever gotten above yourself with a spirit of adventure, turned off and disabled a bunch of default automatic services thinking they are wasteful and consume too much CPU on a slow saturday night, and woke up to find your pc going crazy on monday morning?
I was in a similar situation and it was even worse, at a time when I was cleaning up some adware-related annoyances.
Anyway, what I found out for sure: The disk management and disk defragmenter tools that I started from right-clicking on MYCOMPUTER and MANAGE started working again when I started and changed all default xp home services to automatic again!
Search the MS website for the page on xp home services that start automatically on startup and make sure they are not disabled or manual.
Here is an excellent page that has exactly what you might need at blackviper.com.
http://www.blackviper.com/2008/05/19/black-vipers-windows-xp-x86-32-bit-service-pack-3-service-configurations/

Relieved, but I still have my access privillege issues to get rid of.What a nightmare!