Delete the following file:
%AppData%\Skype\shared.xml
if it says that you already logged in, then delete all the *.lck, *.lock and temp* files.
Or if you are a noob, press WINDOWS key and R then type cmd and copy&paste it and press ENTER
del %AppData%\Skype\shared.xml
To open the folder press WINDOWS key and R then copy&paste this and press ENTER:
%AppData%\Skype\
So Skype 5 isn’t working. What can we do?
Download older version from here.
Use the web version. Go to imo.im.
Or just forget Skype and play some games.

The official Skype for Android not working too. This is part of the global Skype problem since Thursday, May 26th, 2011 11:55 GMT
UPDATE: Working again.
So Microsoft took Skype and now Skype not working anymore.
But only Skype 5. You can still use Skype below v4.2
Download from here: http://oldapps.com/skype.php