Im stuck hellllppp!!!!

Hello,
my computer was given to me by a friend whose company brought more new computers and she dosent have the old password so when i log on i do not get the typical widows display screen with the start menu and so on i get a black screen that tells me to press control alt delete and after doing so i get the windows log on password screen which i dont have the password to. ive tried the old f8 remedy and tried to set it into safe mode that didint work neither did the run normal as before option or something close to that and that did not work ive looked for the administrator feature but it just wouldint work what can i do to get past this password problem?