If you format it will delete everything. So you can't go in the computer and open the disk? If not, it may be corrupted. Try removing it and putting it back it. You could also try on another PC. If that doesn't work, you may have lost them.
Yes, formatting SD card will erase everything. I've had this happen to me (where an SD card works in the camera but not in a card reader). Try downloading the pictures using the camera and USB cable (not a card reader).
Generally, as long as you have not rewritten the original data, you can also recover your deleted files from this SD card.
At first, take off your memory card from your digital camera or smartphone and connect it to your computer or laptop via a card Reader.
And then download a free SD card recovery tool to retrieve your deleted data from http://blog4mark.blogspot.com/2012/12/sd-card-recovery....
This freeware is capable to recover data from all types of memory card and also has helped many people restore their photos, videos, songs and files back.
From now on, you should learn to back up everything important on different storage device all the time.