Is there any important data inside it?
Actually, the format process is quite simple to operate: right click your SD card on "My Computer" and select "Format".
Or if it is not work, you can try another way:
Start => Setting => Control Panel =>Administrative Tools => Computer Management =>Disk Management=> Right click your SD card on the list => format it.
But, if there is a great amount of important data, you are supposed to restore the data
before any format. And nowadays, a recovery program can help you restoring the data. A reliable and professional recovery utility
enables you to restore your images, music, files and other data types from your RAW SD card.
It is worth trying.