Take it that you are selecting the 'R' option at the first prompt. This takes you into the repair console and unless you have set an administrator password then you just need to press enter. However unless yopu know how to use the repair console steer clear. Insteaed of selecting 'R' continue as if doing a new install then select 'R' at the next prompt. This will then do a full repair without losing your file structure etc. You will however lose any Win XP service packs/updates.
I have tried running 'r' repair but it did not work. Everytime I get to administrations password, I press enter as no password has been entered and all I get is the name of the drive that I am trying to repair and no further. any ideas?