I had exactly the same problem, and fixed it by reflashing with the eMMC rom, exactly as explained in this thread. After that I could browse the device with the file manager, and it said 30 GB free or something.

Before I reflashed the eMMC, it said memory corrupted or something. And when I recieved a sms, a popup kept popping up saying no messages can be send or recieved because the memory is full. I could only read the sms once, when I recieved it, and then it disappeared.

The calendar app also kept crashing, and when I scrolled to the desktop which had the calendar widget on it, the phone would automaticly reboot after a few seconds. And when it booted it would say "device storage format unsupported". I could install programs, because they are installed on the other partition. The main 30 GB of the device were corrupted.

But then I found out I also had another problem, because my microphone seemed broken. And I'm not the only one as you can see in this thread. I returned my phone to Nokia today, hoping to get a new one next week.