From what you have written, I assume the computer is booting into Windows and reaching a password screen.
Entering your old password does not work.
It would seem that, since this was a company computer, your previous password has expired. Unfortunately, you no longer have an administrator to assign a new one and enter it into the computer.
What you need now is either an administrative password or a way to find out what it is or to remove it.
The easy way would be to get the admin password, if you know who had it for your former company.
Failing that, you can try to remove the password. See the following web site.
http://home.eunet.no/~pnordahl/ntpasswd/bootdisk.htmlThis page also has a link to other ways to recover a lost password.
The only other option I can see is to format the computer and reinstall the operating system. This would destroy all data on the hard drive and require a Windows installation disk with a valid code to enable you to register Windows.
Best of luck.