No available users

I have just had a new hard disk installed in my macbook. While reinstalling all my applications etc it appeared that the password for my username had become invalid.

So.... I started the macbook from the OS install disk and used the Reset Password utility to rest the password for my user name which appears in the little pull down menu...

but.... on restarting the m/c I get a little login window asking for my username and password.... but the password i just reset is not recognized....

so... I go back to the Reset Password utility on the OS install disk and now am told that there are "No available users" on my hard drive..... so am unable to reset anything


so.... I reinstall the whole OS again, assuming that this will clean everything off my drive and let me set up a new username and password....

but... after reinstalling the hard drive i get the same login window asking for a username and password... which won't accept anything i put in

and... when i go back to the Reset Password utility on the OS install disk I am told again that there are "No available users" on my hard drive....

what on earth do i need to do to break out of this loop just so I can set/reset my username and password?

any thoughts on a solution to this one will be most gratefully received.

thanks