I found a solution that worked easily for me.
My SanDisk 2Gb was offering me only 34Mb and I didn’t even formatted it.
So I tried formatting and nothing worked.
I found this How-to Geek answer and followed the steps and I recovered the whole 2Gb.
Formatted it as NTFS afterward because it is more up to date and you won’t get the “Need to format” message anymore.
At least, I didn’t get it after format.
So here is the address :
http://www.howtogeek.com/170794/ask-htg-how-can-i-reclaim-the-full-capacity-of-an-sd-card/
I made myself a copy of the steps in case it happen again and
I added the lines
"Redo the List disk again and you will see an asterix aside (on the left) of the disk 1 and that tells you chose the right disk."
Right after
“Whatever commands you execute after this point will only make changes to the selected disk; now would be a good time to double check you’ve selected the right disk just to be extra safe.”
Because it would be unfortunate to wipe out all my C:\ drive instead of the SD Card.
Make sure you see the little asterix aside the SD Card Disk number ID and then do a Clean command.
After, you format and there you go.