Now, this may or may not shed some light, but it's worth a run to try and save you from a full re-install of XP.
Download: StartDreck (
http://www.greyknight17.com/spy/StartDreck.zip).
Unzip to its own folder and start the program:
Press 'Config'
Press 'mark all'
Uncheck the following boxes only:
System/Drivers -> NT Services
System/Drivers -> NT Kernel- and FS-drivers
Press 'OK'
Press 'Save' and select the location to save the log file (default is the same folder as the application)
Post the log in this thread.