When faced with such an issue, you’re bound to find the following fixes very helpful:
* Try a different USB cord: Try using another USB cord to connect the Android phone to the PC Restart the Phone and PC: Restart both the Android phone and PC to clear any OS errors that might have been encountered
* Try a different port on the PC: Connect the Android phone to the other USB ports on the PC to be sure the fault isn’t from the PC’s USB port(s) * Check the SD / memory card for errors: The SD card might require a minor check or even formatting in extreme cases. (See How to fix / repair corrupt memory card, SD card or USB drive)
* Enable Mass Storage on the Android phone: When the phone is connected to the PC, you should see a USB icon at the top > slide down from the top of the screen to reveal the menu > Click on Connected as USB Storage > Under USB Computer Connection, Select USB Storage > Press the back button to exit
* Enable USB debugging and Mount SD card: If the USB icon doesn’t appear when the Android phone is connected to the PC then enable USB debugging (Settings > Developer options > Tick USB debugging) then Mount the SD Card (Settings > Storage > Mount SD card)
Source: http://blog.hovatek.com/how-to-fix-an-android-phones-mass-storage-sd-card-that-wont-connect-to-pc-using-usb-cord/
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