1.
Installation Media. What media did you reinstall Windows XP from:
a. Recovery/Restore Partition
b. OEM Recovery/Restore CD
c. OEM Install CD
d. Microsoft Retail Install CD
2.
Process Explorer. Instead of Task Manager, use the program Microsoft should have provided -
Process Explorer from SysInternals (now owned by Microsoft). It will give you a better view of what's going on with your system. Look for processes and/or services that don't need to be running. (In other words review and cleanup list of third party software that automatically runs at system startup.)
3.
Autoruns. The
Autoruns program from SysInternals is one of many "free" programs you may use to control what runs at system startup. (Or you can use "
Startup" tab of Microsoft utility "
msconfig". Access via "Start -> Run -> type "msconfig", select OK -> select Startup tab".)