Hi I hope someone knows what I can do

I have restricted my daughters login details and forgotten my password so i cant install any software etc and every time i try and get in it says i have insufficient privileges to alter use names as I am having to use her login!

How can I get back in as an administrator its an xp laptop dell  inspiron so it doesnt even have an xp disk to reformat the drive is there any way round it or am i stuffed

Grateful for any help

 

Ken