This can go wrong in two places... on the device end and the android end.
When hooked up to USB, there should be in the status notification section
of android a little USB icon (looks like a trident/pitchfork). You need to
click on that and make sure it is set to the USB mass storage mode. By
default it is in "windows media server" mode or "none".

On the other end, it could just be a matter of not automatically mounting
the drive. You can open up a terminal and type 'sudo mount -a' to muont all
connected devices and filesystems specified in fstab. It is also
possible you could need to write a udev rules file for the tablet, but I
don't think you need that unless you are trying to run through the android
debug bridge server (where you are communicating through your device in a
terminal).