Try /opt/nessus/sbin/nessusd -D to start the daemon manually...
When i try to connect to the nessus server, I get an error message saying "could not open connection wtih localhost" and before I rebooted, it was fine. I ran the ldconfig or something that I read I was supposed to run before I run after a reboot. Any help?
So the daemon starts properly (you can see it via "ps -ef|grep nessusd")? Are using the correct port on the client? Are you using the correct username/password on the client?
Nope that just tells you what processes are running.