Bonjour guigui371,
Je ne connais pas le private key et je doute que l'on puisse le retrouver dans le wallet puisque l'adresse n'y figure plus.
la private key c'est en gros une chaine de caractères qui te permet d’accéder à tes bitcoins.
ton logiciel de gestion des BTC (le bitcoin-qt) utilise les private key de chaque adresse pour effectuer les ordres que tu lui dis (envoyer, recevoir).
Dans ta console de commande si tu fais "help" tu a la liste des commande possible et si c'est comme mintpal ou les autres (pas de raison que ce soit différent) en faisant "dumprivatekey" tu obtiens la privatekey de l'adresse souhaitée .
Si il n'y a qu'une chose à sauvergarder c'est ça.....
D'ailleur une sauvergarde de wallet c'est le couple "adresse BTC - Privatekey associée"
wikipedia :
Private key
A private key in the context of Bitcoin is a secret number that allows bitcoins to be spent. Every Bitcoin address has a matching private key, which is saved in the wallet file of the person who owns the balance. The private key is mathematically related to the Bitcoin address, and is designed so that the Bitcoin address can be calculated from the private key, but importantly, the same cannot be done in reverse.
Because the private key is the "ticket" that allows someone to spend bitcoins, it is important that these are kept secure. Private keys can be kept on computer files, but they are also short enough that they can be printed on paper. An example of a utility that allows extraction of private keys from your wallet file for printing purposes is pywallet.
Summary
Any Bitcoins sent to the address 1CC3X2gu58d6wXUWMffpuzN9JAfTUWu4Kj can be spent by anybody who knows the private key in any of the three formats. That includes bitcoins presently at the address, as well as any bitcoins that are ever sent to it in the future. The private key is only needed to spend the balance, not necessarily to see it. The Bitcoin balance of the address can be determined by anybody with the public Block Explorer at
http://www.blockexplorer.com/address/1CC3X2gu58d6wXUWMffpuzN9JAfTUWu4Kj - even if they don't have the private key.
If a private key with a Bitcoin balance is compromised or stolen, the bitcoin balance can only be protected if it is immediately spent to a different address whose private key is not compromised. Because bitcoins can only be spent once, when they are spent away from a private key, the private key is worthless unless more coins are sent to the address.