Installation php 7.0

Bonjour,

J'ai voulu installer php 7.0 en FPM.
J'ai donc j'ai un

apt-get install php7.0-fpm

Mais j'ai une erreur :

Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 php7.0-fpm : Depends: php7.0-cli but it is not going to be installed
              Depends: php7.0-json but it is not going to be installed
              Depends: php7.0-opcache but it is not going to be installed
              Depends: init-system-helpers (>= 1.18~) but it is not installable
              Depends: libc6 (>= 2.15) but 2.13-38+deb7u10 is to be installed
              Depends: libdb5.3 but it is not installable
              Depends: libpcre3 (>= 1:8.35) but 1:8.30-5 is to be installed
              Depends: libsystemd0 but it is not installable
              Depends: libxml2 (>= 2.9.0) but 2.8.0+dfsg1-7+wheezy5 is to be installed
E: Unable to correct problems, you have held broken packages.

Dès que j'essaie d'installer un des packages manquant j'ai une nouvelle erreur de dépendance.

En cherchant un peu sur internet j'avais trouvé qu'il fallait mettre l'extension GPG de Dotdeb.
J'ai donc ajouté le lien dans les sources d'apt puis j'ai téléchargé et installé la clé GPG.
Sans résultat.

Si jamais vous savez quoi faire, j'en serai ravie.
Merci d'avance.

C.R.