Never heard of ADB...
Folders with files of mp3, wmv, mp4, pdf have been disappearing from the SD card after a while also.
It's really odd. Could it be the SD card? I contacted the guy I bought it from on eBay and he says it was ok when he sold it to me...
When I choose 'No' on some transfers, some files play, some files appear to play then close (screen returns to app menu) and some give me the message ' This video cannot be played'
I don't to mess around with any modifications or roots as this device seems to be messed up as it is!
I've contacted Samsung and Panamoz now and I'm looking to return it and get a refund, if not they should send me a brand new one where I'll sell it for a cut price on eBay or Gumtree, or here!