No matter what tool you have to make that tool to work you need to login to some user on the system. It is something like visiting Bahamas without me going to Bahamas.
There are available tools to reset password/admin password when ur system boots. U can create a password reset CD/DVD/Floppy/USB using the tool(s) and let ur machine boot from that particular drive. Voila! U reset admin passwd. Ophcrack is one such tool!!
Please Specify the Following :- 1. Operating System = The thread being in the Windows section , So I assume windows 2. Kernel Version 3. Architecture 4. Remote or Local