Phil,
From a previous newsgroup post by Doug Knox:
<quote>
Click Start, Run and enter REGEDIT Go to:
HKEY LOCAL MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Look in the right pane for a value called Userinit. Its value should
read:
C:\WINDOWS\system32\userinit.exe,
Including the trailing comma. If it reads anything else, double click
the Userinit value and change it. This assumes that XP is installed on
C:\Windows. If not, adjust the command line accordingly.
</quote>
If that does not help, see what startup applications are running. Get
the Autoruns utility (as they call "superset of MSConfig") from
www.sysinternals.com and inspect the startup programs.