Question: Recently I installed Ubuntu 13.04 (x64 bit) and I am new to Linux. In "Ubuntu software center" the right side "install" button is disappearing when I am trying to install software. Instead of "Install" button "Use this source" button is appearing.

"Install" button was appearing previously, but not now. 

already tried with below two commands, still "install" button is not appearing.

```
sudo rm /var/lib/apt/lists/lock
sudo rm /var/cache/apt/archives/lock

```

Please help me how can I get back.

Answer: 
That seems to be an issue of libreoffice-kde package. Looks like it is this already filled bug
<http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=695025>

As a workaround, you either uninstall `libreoffice-kde` **or** disable the kde file dialog in **Tools** > **Options** > **General** by checking **Use LibreOffice dialogs**.
It's come back. I use kubuntu 17.10. When LO was upgraded to 5.4.5.1 (1:5.4.5-0ubuntu.17.10.1) LO crashed on saving any file, existing or new, any file format. In this case the solution was to remove (I used 'completely remove') the package 'libreoffice-kde' (was version 1:5.4.5-ubuntu0.17.10.1)