I had this problem with conversation where all my msg went missing. Yesterday my battery ran flat. I recharged and when I open Conversation, no conversation listed. But when I sms to a contact, all the history text returned. After a while of receiving texts, when I select to delete one msg, all other msg gone.
Another problem, this happened first, any IM msg, no history is stored. Once I close the IM, all history cleared and start fresh history when the same contact start a new IM and IM are not stored in Conversation as well.
I had my internal 32G memory corrupted. This doesnt bother much as I still had 8G external. But conversation problem does as I lost track who I had been chatting on IM!
Hope someone have similar problem and had a workaround to this issue.

Thanks.

Now my Conversation doesnt shows anything in it. If one SMS come it, I can open and read. But if 2 SMS received and on the notification yellow box stated 2 SMS, if I touch the box, Conversation open, both messages gone. I can send SMS thru Phone but the history show last SMS was 29th Dec. After that all messages are not stored.
When I reboot, any sent SMS, a delivery notification are shown again and also all SMS received earlier also got notifications but when open, they all vanish.

Anyone can direct me to how to reflash or reinstall M5 to my N900? The missing SMS and IM are very annoying.