PostgreSQL server failed to start

Hi,
         When i start my postgres. Iam getting this error. I had
installed 8.4 and 9.1
It was working good yesterday but not now.
service postgresql restart
  * Restarting PostgreSQL 8.4databaseserver
* The PostgreSQL server failed to start. Please check the log output.

If i see the log. it shows yesterday's log report. please give me suggestion
Thanks for reply.

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Regards,
Vignesh.T