Encontrei este - O Windows XP PENSA em modo de segurança :
XP assumed to be in safe mode presumably because of the environment variable SAFEBOOT_OPTION that had been set to "NETWORK".
This can for instance be checked by selecting: start-control-system, selecting the tab "advanced" and pushing the button "environment variables". Scrolling the list of system variables should show whether the (cause of) the problem is the same, e.g. SAFEBOOT_OPTION being listed as having a value (whether NETWORK or MINIMAL).
If this is the case, then open the registry and look for every instance of "SAFEBOOT_OPTION" and reset the value from 2 to 0 (do not delete the key alltogether!). The 2 essential places where you will probably find the entry are HKCU - environment, and HKLM - system - currentcontrolset - sessionmanager - environment.
After rebooting however, the keys re-appeared until I removed the key OPTION(S?) at every occurrence of "Safeboot" under HKLM - Controlset001, Controlset002 etcetera, Currentcontrolset - Control - Safeboot (if I remember correctly, the OPTION key appeared under "Safeboot" next to "Minimal" and "Network" and had a value "NETWORK". For some reason that I was not able to determine, after rebooting, the system announced that during bootup it had experienced a severe exception error (I did not see it, however), but the system was fully operational thereafter anyway. After a second reboot, the error did not occur anymore and the services necessary to carry out Windows Update could be started again.