I'm unable to find the user Administrator in the list of the users after selecting the proper SAM database in Active@ Password Changer. Where it is?

Most likely, the local Administrator account has been renamed for security reasons.

Active@ Password Changer always displays the built-in Administrator's account on top (even it was renamed) and highlights it in a Cyan color. Write down this account name to be able to type it in later on, after its password has been reset.