[Q] GalaxyNote1 (no root) stopped mounting internal USB card

Hi folks,

I am a new android user. I have Galaxy Note 1 and it is not rooted.

Here're the specs of my phone:
Model GT-N7000
Android v4.1.2
Kernel v 3.0.31-906407
se.infra@SEP-128 #3

It has a 16 GB external SD card + default internal USB storage. It was working fine till a few hours back. Then Gallery stopped opening and Camera wouldn't start either. There is nothing shown in MyFiles folder. I have checked using ES File Explorer as well and no data is shown in the directories.

External SD card is working fine. But Internal USB card does not get mounted. There is > 500 mb in internal memory. I've moved most of the apps to SD card and removed unnecessary ones.

Here's the break up of 'Storage':

Device memory
Total Space - 1.97 GB
Applications - 749MB
Available space - 560MB

USB storage
Applications - 158MB

SD card
Total space - 14.83 GB
Available space - 2.18 GB

I have cleared Gallery app - cache, rebooted but it doesn't change.

Also, I noticed that when I am trying to back up messages, it waits for external storage card. The card is inserted and mounted but the phone has stopped seeing it as active. I can mount the external SD card on my notebook though.

Can anyone please help. I am starting to get worried