TNS-12541: TNS:no listener

The command lsnrctl start ORCLPLSQL resulted in "TNS-12541:TNS:no listener " error yesterday; I was puzzled (See below).

(Screen -01)

Oracle was working perfectly fine till then; moreover, I had not installed any new s/w at all.What could then be the issue?
A search on Google brought up this page: ORA-12514: TNS:listener does not currently know of service requested in connect descriptor

As listed in that web page, I tried the first one.
The Command, show parameter local listener displayed that tns port has not changed, listener.ora is pointing to the correct port.
Next, I tried tnsping avs.ramanujam.com, which resulted in the same error message.

(Screen -02)

Another thing I noticed was, both starting up the listener and tnsping was taking more time than usual. Next I ran the ifconfig command, I noticed that the ipaddress had changed. (I have to make a confession here. Even though the best practices and the recommendation is that "servers" should have static ipaddress, I had not made it static.) Bang- sound of myself hitting my head  -changed the ipaddress in the /etc/hosts and I was back into business in no matter of time.
Final screen is after successful connection is shown below

(Screen -03)