After adding the ppa and apt-getting plexmediaserver, it briefly said something like "running media server". Then disappeared.
root@host:/etc# ps aux |grep -i plex
root 8757 0.0 0.3 4192 752 pts/1 S+ 12:11 0:00 grep --color=auto -i plex
root@host:/etc# lynx --dump http://localhost:32400/manage/index.html
Looking up localhost:32400
Making HTTP connection to localhost:32400
Alert!: Unable to connect to remote host.
lynx: Can't access startfile http://localhost:32400/manage/index.html
I use the same server and i never installed via PPA, probably there is a bug on that version or something. If you ever need to install any thing ALLWAYS go to the official website first and check if there is a release in the form a deb package.
Just to check, remove the one you installed, and download the one avaliable here http://www.plexapp.com/getplex/ , the latest version is 0.9.7.12.407, you should not have any issues unless there is something else in the middle like some firewall rule that is blocking all incomming connections to the localhost.