wont read external micro card

It has a spring loaded locking system...Did the card lock in its place securely....?? It is always better to switch of the device before inserting an "External Card" or "SIM Card". You can try to "Factory Reset" (navigate from "Settings") your device (make sure you take back up of all your contacts, photos, messages, Apps...etc). If it still doesnt work then try reading your MicroSD card thru a "Card Reader"....if it fails to read, then your card is faulty. If not take your Tab to "Service Center"