Why can’t I get win xp pro to boot in safe mode to access the command prt?

I think my DD has acquired a virus and now I’m trying to load win xp pro in safe mode to try to get to command prompt and restore the system. But when I try the F8 way of doing this (it’s a Dell desktop)I get to the ctrl-alt-delete to begin screen and then the password, at which time the personal settings start loading, the virus loads and the system freezes. Any suggestions?