Ubuntuソフトウェアセンター：問題を解決できませんでした。パッケージが破損しています。

Ubuntu 14.04 LTSでパッケージソフトウェアセンターが見つかりません。

端末経由でインストールしようとしましたが、次のエラーが発生しました。

ravip@LP204:~$ sudo apt-get install software-center
[sudo] password for ravip: 
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:
 software-center : Depends: software-center-aptdaemon-plugins but it is not going to be installed
                   Depends: python-gi but it is not going to be installed
                   Depends: python-gi-cairo but it is not going to be installed
                   Depends: python-aptdaemon (>= 0.40) but it is not going to be installed
                   Depends: python-aptdaemon.gtk3widgets but it is not going to be installed
                   Depends: oneconf (>= 0.2.6) but it is not going to be installed
                   Recommends: software-properties-gtk but it is not going to be installed
                   Recommends: sessioninstaller but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

すべてのDependsパッケージRecommendsがインストールされ、最新の状態です。

どうすれば解決できますか？