Used Apple OS Install disc to change "Admin" password but the app could not find the admin login. Any suggestions?

When trying to link an e-Mac to a HP Server using Microsoft XP operating system, the administrative login and password was lost. Don't know why. When I tried to use the admin login to access the computer but was told that either the login name of password is incorrect. In attempt to gain access, I decided to use the OS 10.4 Install disc to change the password hoping the password was somehow changed. However the Install disc could not find either of the 2 logins that I created.