Are your pictures 'stored' on the removable SD Card in your device?
If so, it may be that the card has become corrupted.
You may (stress only may) be able to 'recover' the pictures by placing the SD Card in a card reader connected to a PC and then using Recuva (here is a link http://download.cnet.com/Recuva/3000-224...) to see if it can restore them for you.
Remember to use the correct way to remove the SD Card from your device, i.e. either turn off your device and then remove the card or go to the Storage area in Settings and 'unmount' the external SD Card. Never remove an SD Card with the device turned on unless you unmount it first.
If you can recover your pictures, I suggest that you replace the SD Card and also think about saving your pictures to 'the cloud' or backing them up often in case you have other problems with your device.