I've been using Skype for Linux for a while now. When I tried to use it today, it would freeze and force quit every time I did anything. I am also getting the error message that Skype is not installed, yet it still appears in my launcher, although it does not appear in the list of installed packages. How can I fix this?
most probably your installation corrupt somehow. Try to uninstall skype by this, should be enough:
sudo apt-get purge skype*
or follow this question: (Uninstalling Skype 4.1 from 12.10) and then install it again via software center or by
sudo apt-get update sudo apt-get install skype
if update does not help probably skype is missing in your repo, then you can try to add it. Skype is in partner repository, so please check if you have canonical partners repository enabled.
If this does not help, there is a ugly way to install skype from .deb package by downloading it from the web. here are some steps that could help you: (Can't install Skype through Software Center 12.04)