Formatting media wipes all the data off of it. Therefore, before you format (and thus erase) the SD, make sure you still have the original files on the windows machine. You might have accidentally "moved" them to the SD card instead of "copying" them to it.
Once formatted FAT-32 virtually any machine should be able to read it - windows, linux, mac...
Using a PC, how do I check what format the card is now?