My Zte Blade

Solution
Is this a new card? or a card you have used in a different device?

If it is one that has been used before, it may not be formatted correctly to work in your phone. Also, if the card is larger than 32 GB it may not work in the device, as it has that as its max limit.

It is also possible that the SD card, if older, may just be damaged. They do not last forever. Should that be the case, then you can't fix it, only replace it.

If the card is not dead (so to speak) then you should try moving the data on it to another device. Say a computer, which should be able to read it, and then try reformatting the card and putting it back in the phone (without adding the data back just yet). If it works, great, you can move your stuff back on it. If...
Is this a new card? or a card you have used in a different device?

If it is one that has been used before, it may not be formatted correctly to work in your phone. Also, if the card is larger than 32 GB it may not work in the device, as it has that as its max limit.

It is also possible that the SD card, if older, may just be damaged. They do not last forever. Should that be the case, then you can't fix it, only replace it.

If the card is not dead (so to speak) then you should try moving the data on it to another device. Say a computer, which should be able to read it, and then try reformatting the card and putting it back in the phone (without adding the data back just yet). If it works, great, you can move your stuff back on it. If it doesn't work, then you have lost nothing. Just get a new card and then move the data onto that one after it is working in your phone.

A side note, I always suggest backing up anything on a phone and/or card to a cloud account or a computer, so you don't lose anything. In the case of your phone, since it is a bit older, you definitely should be backing up your personal data.
 
Solution