Can you tell us what type of phone you have and what size and type of SD card you have?
Also can you tell us what you have done to prepare or load the card for your phone.
To be honest your files will not show up on the card even if you put it ino the computer again as when you selected the format function it reformatted or wiped all data from the card and made it ready to have fresh data put on it.
The correct procedure would have been Reformat the card from the phone so it is setup in the right way to be read by the phone then take it and plug it into the computer and load the songs etc onto it, So if you put the card into your machine and re copy the files to it your phone should then read it.
Just remember the ony time you wish to reformat the card is when you wish to wipe it blank.
Let us know if you need more info.