There is a hidden administrator account.
You can log on it and you can change or remove all the other passes of your comp without knowing the previous passes. Just type ctrl alt del twice and then type Administrator on the account name and you can enter. If that won't work, restart the computer and toggle the F5 button.You will get screen that will ask you if you want to boot with command prompt, choose it and then type net user, then press enter
# Then again type "
Net user [Username of the Account]*" then press Enter, without the ["], and quotes. Make sure you spell the username correctly, and you have the '*'
# To change password press enter and after that tieler south * Reset password to what ever you want.
If that won't work, go to this link ..more suggested info on the replies