did you format the SD card in the computer? I would reformat the card in the phone.
Last time I used it to transfer photos and videos to my computer was last summer, and that wasn't the first time I did it. What I mean by that is that the memory card was already formatted, and I believe I formatted it in the phone. Even if I wanted to reformat it, it's as if the phone doesn't recognize it. Like I said, the words "Manage Memory Card" are not active --they appear in a light gray color in my phone screen, whereas "Clear Phone Memory"and "Used space" are in dark black. I don't want to clear the memory since I'm afraid I'd loose all my data.