I can't open my inbox?

My Nokia 6300 was made for vodafone and i changed its software to make it sim free, i've been using it for 10 months but i had a problem 2 days ago, i can't open my inbox or my memory card and when i switch it on it goes off from time to time and when someone rings me they found me out of service, i do care about the txt messages iin my inbox and i don't want to lose them. i'd like to get help how to open my inbox and if it's possible to transfer them to the memory card or the PC?
Adel Muhammed, November 2009
link Click here to see other fixes for Nokia 6300.