Postgres won't start. Nothing in the log.

I just did an upgrade on two of my servers (the main and the
failover). The main went OK but the postgres on the failover won't
start.

Unfortunately there is nothing anywhere telling me what the problem
is. The log file is empty, there is nothing in the /var/log/messages
or /var/log/syslog either. The only output I get is this.

* Starting PostgreSQL 8.3 database server
 * The PostgreSQL server failed to start. Please check the log output.


What can I do to figure out why it won't start?