OK. So when I try to install a something in the terminal, I get:
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
I then try using apt-get -f install, but then:
dpkg: warning: there's no installed package matching pidgin-facebookchat:amd64
When I try to download pidgin facebookchat (from the Software Center) I can't to that either, cause I get a popup saying:
Items cannot be installed or removed until the package catalog is repaired. Do you want to repair it now?
I click repair, but it keeps asking me about it. Therefore I can't either install something from the Software Center.
sudo apt-get -f install? Also, see How do I resolve unmet dependencies?