Re: Android phone says 'Damaged SD card' but my PC can read it
Copy
everything on the card to the PC. Put the card into the phone and reformat it. Put it back into the PC and copy the folders back. Put the card into the phone (remember to use "safely remove" before removing it from the PC and unmount it before removing it from the phone) and see it it works.
If not, format the card again (in the phone), and start copying one folder at a time, putting the card back into the phone after each folder.
Either you'll copy all the folders back and everything will be okay, or one folder will give you a problem. If that happens, delete that folder from the card, finish copying the rest of the folders to it. Then create a folder of the name of the bad one on the card (you can use the PC - right-click on the card/New/Folder and name it (case counts). Open the folder on the PC, open the folder in the card, copy a file from the PC to the card, put the card into the phone and see if it's okay. Keep going until you find the bad file, then delete it and copy the rest.
It's a long process, it could take hours if you have a lot of folders and only 1 file is causing the problem, but the only other way is to lose everything on the phone (you'll still have all the copies on the PC) by just formatting the card, and you probably don't want to do that.
If it's an S3 phone and a SanDisk card, and you still can't get it to work on the phone, contact SanDisk
SanDisk microSD Tech Support (there's a live chat at the right). Samsung created a problem that SanDisk worked around in their later cards, and they might replace the card for you. I never asked that question because I never had that problem, but the reason I buy only SanDisk cards is that they make good ones and they're an easy company to work with when you have a problem.)