I found this site, is this what you did to your SD card?

How to Format Your Cards
In the windows operating system formatting is very easy. You will need a card reader to put your card in. These are inexpensive devices and use only 1 USB port and do not require plugging into the mains power supply.

Open Windows Explorer (Windows Key + e)
Right Click on the Flash Memory Card Drive
Select “Format…”
Choose the File System (FAT or FAT32, your PDA will not read NTFS) you want from the dropdown box
Choose the Allocation Unit Size (4096 byte or 4KB is good) if you are given this option
Uncheck the “Quick Format” button
Give your card a name if you so desire
Click the “start” button
You will be presented with a summary of the results at the end