USB Drive Lost Data?

Hello,
I was using my SecurView usb drive today with no problem at all, I was going through the pics and movies I have on there when a friend came in and said we had to go to dinner. Anyway, being in a hurry I just closed what i was doing and removed the USB drive. I got back and plugged it in and everything seemed normal, then the Pics section was showing no files! The drive Properties shows 1.56 gb of used space but less that 1 gb of my things are on there! All the pics and the short clips I had on there are gone. I assume they are still somewhere on the driver since its saying so much is being used but what should I do to get it back?