Ran into this today on both Windows and Linux. Plugged it in, and nothing. re-installed drivers on Windows, still nothing. Realized my CyanogenMod 10.2 phone was unable to mount the cards completely ! Here's a quick fix.

To mount sdcard0, open terminal emulator and run the commands below:

su
echo mkdir /storage/sdcard0 > /data/local/userinit.sh
chmod 700 /data/local/userinit.sh
exit
exit

OP:
[Cm10.1] - Internal Sd Card Don't Mount - Samsung Galaxy S II Nightly/Experimental - CyanogenMod Forum




It may just have been my frankenphone having a melt down - or this could be an actual issue. But it's definitely here for reference if you ever run into mounting problems .