Recovering lost files?

Central Coast, Calif.
I installed a new hard drive into my computer and set up XP on it. then hooked up my old HD to copy files onto the new drive and use the old drive as backup. everything was ok for about a week and I got most of my stuff copied over. now all of a sudden windows says my old hard drive is corrupt and I can't access anything on it. is there a way to retrieve the old files? any freeware?