ResolutionFirst of all make sure that Postgres is not running:
ps ax | grep postmaster
Check Postgres log (by default logs stored in /var/log/pgsql, on Fedora Core /var/lib/pgsql). If you see the error like:
postmaster: cannot create UNIX stream port
LOG: StreamServerPort: bind() failed: Address already in use
Is another postmaster already running on port 5432?
If not, remove socket node (/tmp/.s.PGSQL.5432) and retry.
This socket should be deleted:
rm -f /tmp/.s.PGSQL.5432
Try to start Postgres again. If it doesn't help look into the logs for new errors.