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Can you tell us exactly what hardware you have? What reader? Is the reader built in to your computer, or does it attach via USB (or otherwise)? What kind of mobile memory is this? Are you talking about an SD card? CF? A USB flash drive? A RAM add-on? Also, assuming this is a kind of memory that can be put into the reader while the computer is turned on, please open a Terminal window (Ctrl+Alt+T) and run sudo parted -l and dmesg | tail. Then put your memory in, wait about 10 seconds, and run them again. Please edit your question to report the results, and tell us about any differences.
Sounds like you might need to mount your drive. This is a fairly general topic, so check what mounting is here and how to do it here, or search for more links on your own.
sudo parted -l
anddmesg | tail
. Then put your memory in, wait about 10 seconds, and run them again. Please edit your question to report the results, and tell us about any differences.