You have to individualize your system, you can't just copy files.

Clean install is the best option. But what version of WMP did you install? Was it WMP 9 or WMP 10.00.00.3646?
Have you updated your WinXP after the installation (correct answer - no)? Have you disabled automatic updates?
Have you installed any updates or hofixes?

If you decided to uninstall any updates or hotfixes, make sure you reboot when it says to after each uninstall of the update or hotfix.

One more thing for Yahoo! Music Unlimited users:
You have to install wmp 10 v3646 after the installation of yahoo music because yahoo music installs Windows Media format runtime that drmdbg doesnt support.
When installing wmp make sure that you install the format runtime so that it replaces the default format runtime that yahoo music installs.