Contact details not shown in phone memory

Hello,
i am using nokia 5310 but suddenly my contact details gone. if i would like to save any items in contact . contact details not saved in phone memory. and massage is showing empty phone memory.i do not understand whats wroung with my mobile.pls tell me how can i restore my phone memory contacts item saved in phone memory but it does not shown in phone memory contact list. pls give me appropiate reply