Hello and welcome to the Sony Forums 
Do any images appear when the card is inserted into a PC using a memory card reader?
If there is a chance that the memory card has somehow been damaged or that the data has become corrupted, it may be worth checking out the free tool that Sony offers to see if memory card data can be retrieved - I cannot guarantee that this will work but this method has recovered some 'lost data' for other users in the past:
http://www.sony.net/Products/memorycard/en_eu/datarescue/index.html
Thanks,
Simon