It is possible that Windows is simply hiding the drives because there aren't any media in them. I know this is typical behavior in Windows 7 and you can change it, however I believe it is the default. Try inserting an SD card (or something that it should be able to read) and see if it is recognized. What should happen is the drive should appear in My Computer and you should be able to see the files.
The setting that controls this behavior is under Folder Options, under the View tab. There is a checkbox under the hidden files and folders radio buttons labelled "Hide empty drives in the Computer folder". It is likely checked on your Windows 7 installation.
If it is unchecked, or inserting a card doesn't do anything, you'll want to see if the drives are listed in Device Manager. If they are and they report errors, let us know what they are. If they don't show up, try rescanning for hardware changes (there's a toolbar button under Device Manager that does it). If it still doesn't show up, it could simply be defective.
I would place my bet on the fact that the drives are simply hidden since they don't have any media inserted in them yet, though, and that the device itself works fine.