Unlocking A Password Protected File

I had a computer about 6 years old.
i disposed it but i kept the hard-disk
since, the Login ID of my computer was password protected…
now i am not able to work on those files since they are password protected.

How should I unlock the files of the hard-disk so that i can work on them?

OS of my old computer: Windows XP
My current OS: Windows 7

Please HELP!!!