Cannot mount SD card, with error "SD card safe to remove"

I have an HTC Desire S, which my cousin bought for me from China. Android version: 4.0.4; HTC Sense version: 3.6; Software number: 1.0.0.S510e The MicroSD card no longer works. Whenever I reinsert it, I get the message, after a few seconds, "SD card safe to remove". I've tried reformatting it and have run fsck on it. I think the card used to mount read-only before, as it used to unmount whenever I took a picture; this started happening after the most recent update. I kept trying to take pictures and reinserting the card would fix it but it seems now it won't mount. How can I fix the MicroSD card so it'll mount?