Is the "missing" the Toolbar buttons on the Taskbar the QuickLaunch, or is it SystemTray icons? If its the QuickLaunch .. right click on the Taskbar and select it.
If you are referring to Taskbar Buttons appearing in the middle of the
Taskbar proper, as companions to open window programmes, then this would
help: http://www.kellys-korner-xp.com/xp_tweaks.htm
Line 240, Lt. side. (Courtesy of MVP Kelly Theriot)
I have assumed that you have already run scans for viruses and any other
malware but
have found nothing.