Keyboard

The keyboard does not work at all
i turn on the computer and it boots up coming to halt on a user name requiring a password. The mouse works and on clicking ok another text box asks for the password.
I have tried replacing the keyboard with one that I know works before and after.
As the keyboard does not work at all i can not use any of the keys.
Is there a work around for this problem. the O/S is XP Professional.