On my galaxy S3 I just bought a microSD card for 20 bucks, it has 8 gb of memory and you can just drag and drop files and they will be added, simple as that.
Try taking out the battery and the SIM card and then putting them back in and restarting it. But if it is already broken you may have just bought a faulty one...
If it is not charger, try removing the battery and then putting it back in. This works for me sometimes but you probably need to replace your battery completely.