Well, there may be a couple of things at play here. If you mounted the memory on a pc but failed to un mount before pulling the usb cable? It's possible to corrupt the memory. If this is so and your pc can still see the memory when attached, this has worked for me-
Open up command prompt (start->run->cmd.exe) and type
chkdsk /X /F <SD card drive letter>
If the devices memory is mounted as X:, use the following command:
chkdsk /X /F X:
This may restore function and recover your data. If this does work? Remember to un-mount the memory (either via the pc or the tablet) before you unplug that USB cable. If this doesn't work, you may need to reformat or do a complete data reset on the device. If that doesn't work? There may be a hardware problem that requires contacting the seller/manufacturer.
Good luck!