iphone4 - says i have 6.9GB of photos but nothing in 'photos'

I'm desperate for some help here!!

I have an iphone4, had massive dramas with it this morning, got a new battery put in, now seems to working fine. . . BUT

I turned it on, my lock screen and home screen are both personal pictures that I have taken, my notes are all still there, my calender adds are all still there, but my photos are all gone!

However, when you look at usage, it says that I have 6.9GB of photos on my phone, but they aren't in the camera roll!! I have plugged it into my PC, and the DCIM folder is empty!! Where are all my photos? I'm terribly slack and havent backed up since Feb this year. With over 1200 photos on my phone, I'm a little upset they are gone, but not convinced, especially as my lock and homescreen are both photos that I have taken and stored on my phone.

Any suggestions?? I have updated to the lastest software version (6.1.3). I cant plug into itunes at the moment as my laptop is in the repair shop and I cant install it on this computer (work computer - no admin rights).

Thanks.