k 750i - cid 36

when the phone is on: 'insert correct sim card'

i've been reading a lot, but just don't get really well wich files I need... do ihave to extract them ? different files ?
perhaps for you all silly questions, but you have to know that one week ago, i didn't even know that there existed something like 'unlocking phones'
so, it's really great that i can get some help...