you could try to reformat the card,or if you use linux it will delete wma files,that phone will play a lot of formats inc ogg and m4a.
my k850i crashes just like yours ! i start my phone then put the m2 card in,this seems to work,or buy a new card(very cheap now) and start again,these new phones seem to like new cards. oh always click safely remove before disconnecting your card from your pc or it wont be properly formated.
markyboy
June 2008