Hate to be the bearer of bad news.
But sounds like your EMMC has become dislodged from the mainboard.
Seen a few like this on the Nokia forum.
All showed the same symptoms as a result of being dropped/knocked severely.
You could be looking at a costly repair job, unless you can claim on the household insurance.

EDIT: Just read your post in the other thread. If you didn't drop or give the phone a bad knock then that is some weird memory corruption.