我无法在 Bionic Beaver 中启动软件和更新中心。不会打开任何视频应用程序。我尝试手动安装软件中心并得到以下输出：
neil@neil-ThinkPad-T420:~$ sudo apt-get install software-center
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package software-center is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'software-center' has no installation candidate
我不是技术专家，几乎无法遵循简单的终端指令。我需要帮助。