OP posted:
I tried to manually start Tor (by typing /usr/sbin/tor
in the terminal) and afterwards Vidalia and it works perfectly.
From the documentation of Vidalia:
I Can't Start Tor
The most likely reason that Vidalia could not start Tor is because
Vidalia is looking for your Tor installation in the wrong directory.
You can tell Vidalia where Tor is located by updating the Tor
Executable option in the general configuration settings. Another
possible reason that Tor cannot start is because there is already
another Tor process running. Check your list of running process and
stop the previous Tor process, if you find one. Then, try running Tor
again.
If that did not help, check your message log to see if Tor printed any
information about errors it encountered while trying to start.
Vidalia Can't Connect to Tor
Vidalia manages Tor by communicating with it via Tor's control port.
The most common reason that Vidalia cannot connect to Tor is because
Tor started, but encountered an error and exited immediately. You
should check your message log to see if Tor reported any errors while
it started.
If Tor is listening on a different port than Vidalia expects, Vidalia
will be unable to connect to Tor. You rarely need to change this
setting, but if there is another service running on your machine that
conflicts with Tor's control port, you will need to specify a
different port. You can change this setting in Vidalia's advanced
configuration settings.
Tor Exited Unexpectedly
If Tor exits immediately after trying to start, you most likely have
another Tor process already running. Check the message log to see if
any of the last few messages in the list are highlighted in yellow and
contain a message similar to the following:
connection_create_listener(): Could not bind to 127.0.0.1:9050: Address already in use.
Is Tor already running?
If you find an error message like the one above, you will need to stop
the other Tor process before starting a new one with Vidalia. On
Windows, you would need to look for tor.exe in your Task Manager. On
most other operating systems, the ps command can help you find the
other Tor process.
If Tor had been running successfully for awhile (that is, longer than
a few seconds), then you should check the message log for information
about any errors Tor experienced before it exited. Such errors will be
highlighted in either red or yellow.