Restart failed with 'service postgresql restart'

Help me start the server.
As I mentioned in an earlier post today (subject: password
authentication failed for user postgres), 'service postgresql restart'
had stopped the server but  *server
start failed*.

Step wise list of commands to be given would be great!
Do I need to login as postgres?

Being new to PostgreSQL, am looking for some hand-holding.

Thanks
Viv