Cannot log in as administrator

My PC is having problems trying to load my administrator
settings whenever I log on to it. It freezes up. I tried
to do it also in safe mode the same thing happens. Using
my guest account does not help me in anything since I dont
have administrator privileges. I also tried re-installing
XP from my CD when logged as a guest but it doesn't do
anything when it prompts me for the adminstrator's
password. I've tried almost everything I know but it won't
work.

Thanks for your help.