Try running a scandisk from a win98 startup floppy (in dos prompt). Also, check FDISK to see what kind of partition you have. If you have an NTFS partition on your old disk, you will not be able to see any files on the other disk until the disk is formated to FAT16 or FAT32.

If you get numerous errors during scandisk, it is likely that drive has failed.

I see a lot of people who change to a new hard drive and keep the old as a backup and end up loosing their data. If you have a drive that is less than 6GB, it is likely that it has ripened to an old age and will need replacement soon. Hard drive also become sensitive with age (as well as the older drives are not capable of the same abuse as the new ones) and they typically get disturbed enough during install of the new drive to cause them to fail. This is why I alway recommend backup to CDROM rather than hard disk when installing a new hard drive and OS.

Good luck.