Pictures randomly became unreadable?

I had a bunch of family pictures on a folder in my computer and no about half of them are not able to be opened up. It just randomly happened. They are JPG's. This seems to happen on my camera sometimes too. I have a nikon dslr and sometimes pictures I take come up as red x's! Wtf

Your card is corrupted. Replace the memory card.

Did the pictures on the harddrive open previously? If so, you have bigger problems than just the card. Try opening them in another application and see if they'll open. Also, copy some photos that have opened without any issues to a separate folder. See if they all open. Then upload some photos from the card into that folder and see if any problems develop. The card may have corrupted the files on your computer. Very weird problem in that it is effecting both the card and the harddrive.