help with reaching command prompt dos w XP

I have a Toshiba Tecra A8 ez8313 laptop and need to clear my system registry in dos screen.. I get to the point where i start PC with command prompts and hit enter but all that does is run a list og the loading drivers and then starts the PC in safe mode ...I cant get it to go to the C:\ comman prompt ...I am running XP and it will no longer accept my password ... I have been told a few differnt things to try during the start up such as pressing the page break key ..... or holding the windows key and R at the same time none of them pull up the command prompt ..please help ... if anyone might know another way to solve this passsord issue please let me know

i cant with windows xp ... still needs admin password which it wont aceppt for some reason... and my boot disk is MIA