N97mini memory card suddendly lost all texts msgs

Do you delete them unintentionally?
You can try a memory card recovery freeware to get back your data as long as you have not saved new file on this memory card.
Sometimes, the files on a drive or memory card can be invisible because of virus attack, or logical damage. Therefore, at this moment, to recover the data back, you need a data recovery program. That freeware ahs ever helped my friend recover his data successfully. I believe it will help you, tool.

Give it a shot: -http://blog4mark.blogspot.com/2013/01/memory-card-recov...

Note: You should keep all your important data backed up on a different drive or memory card in the future.

No, the battery had gone dead - i plugged it in the charger - turned it on as normal and all my texts had just vanished, along with some photos. I will try your suggestion - i called nokia as well and they were hopeless with any advice