pywallet.py --dumpwallet --datadir g:\  --wallet=wallet.dat --recover --recov_device=g:\wallet.dat --recov_size=40Gio --recov_outputdir=c:\recover

This is what I used, if you want a file with the keys (what I did) add a >> dump.text at the end.  You will see nothing on the screen but you have to enter newpassphrase, oldpassphrase, enter
It will scan the drive (make sure the ##Gio is bigger than the drive) and dump any keys it finds to the text file.  You can then take the private keys and import them into a new wallet.