Why did my sd card suddenly get corrupted?

So I have a samsung star GT-5230 and I got my 2 gb sd card out so i could scan it. When I attached it it said scan and fix.....which I did....And then I opened the removable file folder. But all the videos songs etc folder had gone hidden..... I displaed them from folder options and scanned my card for viruses....but now all my 'hidden' folders have turned into .sys files which wont open!!!!!!!! I cant lose all my data....I put the card back in but when I play the video it says file doesnt exist WHAT HAPPENED?????!!!!!