I can't access the internal SD Card (8GB) on my Wayteq x-tab 80, with Android 4. The device is not rooted, and worked perfectly fine until yesterday. I could access the SD card from the tablet, and also from my PC when connected with USB. Now it doesn't work either way. I checked in the Settings, and it seems like the SD Card is Unmounted, but even after clicking on Mount it doesn't do anything. I did a factory reboot, it didn't help.

I'm not a tech expert, so I can't figure out what's the problem. Any ideas?