For slaving a drive in another system the Windows installation on the next case has to detect and install the drive you are trying to save files from as a new hardware. In the device manager once slaved on the middle connector look for the second drive there. Try the right click and uninstall option and restart the system to have Windows on the primary load the drivers needed. It should then be seen as a new logical drive with a letter assigned in MyComputer or through Windows Explorer.
If that still fails to make the drive fully accessible the second option is to boot from a live Linux distro on cd where both hard drives as well as the optical drives will appear as desktop shortcuts. You simply open each drive icon for copying files then. But the Live distros are effective once you get familiar with the differences.
It sounds like the current partition on the drive has become inaccessible and you will need some tool or live distro to avoiid losing the files. Have a friend who runs Linux or ar least a cd writer. The Live distros only cost a cd-r to use. To burn iso images to cd-r BurnOn has a free version available at
http://www.burnworld.com/burnoncddvd/ This one works great for GParted live as well as the different live distros.
For information and a tutorial on Knoppix as a first aid kit for Windows,
http://www.shockfamily.net/cedric/knoppix/ and
http://www.troubleshooters.com/linux/knoppix/knoppix_rescue.htm are good resources.