I can't see the source list in iTunes.
toonz has solved this issue for many folks. Here is the short version of the solution:
OK, let's try deleting the preference files with the theory that something has gone wrong and the last known window position for the main iTunes window has been set to something off-screen.
C:\Documents and Settings\<username>\Application Data\Apple Computer\iTunes\iTunes.pref
C:\Documents and Settings\<username>\Local Data\Application Data\Apple Computer\iTunes\iTunes.pref
You might have to turn on "show hidden files" to find them. (Right click "my computer", select open, select Tools menu -> Folder Options. Select View tab, "show hidden files" radio button is in the center scrolling panel.) Delete them. This will force iTunes to run the setup assistance the next time you run it and you'll have to go back and set any preferences you've changed from the default. But this should hopefully make the window appear intact on your main screen again.