Password issue at logon

I installed Vista on my main pc. When I went through the setup, I chose not
to use a password to logon. I went to logon a few days later and it asked me
for a password at the logon screen. It has locked me out. I have tried
booting up in safe mode to try it that way, but the Admin account is not
enabled and it says my account name and/or password is incorrect. I have
sinced then installed it again on another hard-drive in the same computer
just so I could access my files. Is there a way to go in and fixed my
problem so that I able to logon my original installation?
--
Pcguy