How to disable scan at boot?
Could you please start regedit, go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager, select the value BootExecute and export it to a file? If you could post the file as an attachment here, I would like to check what could be wrong there.
In XP, if you press F8 when starting Windows and select 'Last known good configuration' from the boot menu, the boot scan should not be started.