If your ajenti panel can’t start at 8000 port, first that you should do is watch debug logs with command:
ajenti-panel -v
If you get at the end error like that:
ERROR Could not bind to (u'0.0.0.0', 8000)
You should do the following:
apt-get install aptitude aptitude install python-dev aptitude install python-pip pip install passlib pip install gevent --upgrade service ajenti restart
After that, your problem will be solved.
Information at Ajenti Issue Tracker