Problems, solutions and tweaks

If the whole computer is stuck and no command works go to console and open the terminal than kill applications or the entire session: see this post.

If the wireless is stuck as if disabled by hardware (it happens in some laptops when you use the wireless button a lot) and you cannot physically enable it,  try in Terminal:

sudo rfkill unblock wifi

When a program freezes or something you can go to System Monitor or Task Manager and terminate or kill the process. Install these utilities in Synaptic Package Manager. The lightest is "lxtask".

Some Terminal commands need root access. Type in Terminal:
sudo su

To access root in File Explorer, eg Thunar, type:
gk sudo thunar
Now you can modify your system files - so you risk ruining your system!

VLC Player might stop working (usually if you mess with its files)
To solve: delete vlc folder from username/config folder. Reinstall maybe.
I once forgot what to delete and tried to correct VLC by deleting in root all vlc files in /usr/bin/vlc, /usr/lib/vlc, /usr/share, and /etc folders. DON'T DO THAT ! But in case that it happened already and the installation would be as impossible as the uninstallation, go to Terminal and when trying to install/uninstall VLC (sudo apt-get install vlc) you will be informed what is the program or driver related to VLC that creates that situation (in my case was one called "vlc-nox"). Uninstall and reinstall that one in Ubuntu Software Center. Then reinstall VLC.

Flash Player seems to be missing in Firefox or Chromium although it is installed and reinstalled.
SOLVED like this:
download ADOBE flash as archive (click to install go to website and try to get the tar.gz archive)
- unpack
- take file and put it in /usr/lib/mozilla/plugins ('gksudo name-of-file-explorer' to open in root)
- do the same in /usr/lib/chromium-browser/plugins
(try the same for other browsers if needed: works in Opera - /usr/lib/opera/plugins)

solution inspired from here

Remove unwanted ppa (found it here).
Install GetDeb repository - install this deb
sudo apt-get install ppa-purge
to remove a certain ppa:
sudo ppa-purge PPA 
How to make the Xfce xkb keyboard layout plugin to remember settings after reboot.
I found two files involved in this: /home/user/.config/xfce4/xfconf/xfce-perchannel-xml/keyboard-layout.xml and /home/user/.config/xfce4/panel/xkb-plugin-43.rc (the last number varies in the name) I have seen that the second has the options that are created when you change settings, but these are not saved on session logou. So the other one has to be edited.

First make the desired settings in Settings Manager/Keyboard and in the plugin options. Then edit the two files mentioned so as to have th same options. In fact the xml file is the one that contains the data to be loaded after logout, but it does not contain the shortcut to change layout. This shortcut will be remembered if the other data in the rc file are not different from those in the xml file.

 To fix Skype video in UBUNTU 11.10

Paste in Terminal  to create a blank file :

sudo gedit /usr/local/bin/skype

There, paste the following to make it a bash file:

LD_PRELOAD=/usr/lib/i386-linux-gnu/libv4l/ /usr/bin/skype

save and close
Now to make the file executable, copy and paste the following line into Terminal.

sudo chmod a+x /usr/local/bin/skype

start skype
thanks to this source, including the change suggested by JuliusP0pp in his comment there

To create shortcuts for trash and delete stuff - this post here.