Cell phone memory card?

Hello:)

I recently got a new cell phone ( purple LG reveal ) and I have it for about a month now and well I was taking pictures and then I took a video and I was going to play it to show my friends but there was a big question mark instead of the picture so I tried to delete it but it wouldn’t delete so I restarted my phone and the whole memory was gone.. when I tried to take a new picture, it said, “ saving to memory card “, but the memory card was empty.. I have NEVER dropped it or got water into it. it has been in safe condition. when I try the memory card on my sisters phone it says that a picture cannot be saved onto the memory card because its full but even on her phone it shows the memory card is empty… I took the memory card out so it doesnt do any damage.. tomorrow ima try my boyfriends memory card and he said he will try to fix it but what do you guys think?

Thank you xx