Help - all user acounts have expired!

I installed Mandrake 8.1 awhile ago on a spare hard rive for my laptop.
I had to use my Windows hard drive for a project, so I have not used the
Linux
hard drive for a few months. I tried to log on to the Linux drive today,
and found
that both my root and user account passwords have expired! I cannot log in
to any account.

I tried to set the date back a few months during boot-up, but the OS
keep setting
the date back to today, and I still cannot log in.

Do I have to fdisk and then reinstall, or is there a way to "break into"
the system and log into the system?

Thanks!

Mark