Server 9.1 doesn't restart and no output/log - data files seem corrupted

Hi,

The server was running correctly.
I didn't changed the configuration.
I did an apt-get upgrade and it didn't restarted.
The problem is maybe not related to the upgrade but appeared during the
restart.

I did the same upgrade on another (very similar) server and didn't have
any problem.
The configuration files and files permissions are the same.

The PostgreSQL packages that were upgraded:
postgresql-9.1:amd64 (9.1.8-1, 9.1.9-0wheezy1)
postgresql-client-9.1:amd64 (9.1.8-1, 9.1.9-0wheezy1)
libpq-dev:amd64 (9.1.8-1, 9.1.9-0wheezy1)
libpq5:amd64 (9.1.8-1, 9.1.9-0wheezy1)

The commands I tried to start the server:
# service postgresql start
[FAIL] Starting PostgreSQL 9.1 database server: main[....] The
PostgreSQL server failed to start. Please check the log output. ... failed!
failed!

# pg_ctlcluster 9.1 main start
The PostgreSQL server failed to start. Please check the log output.

There's nothing in the log files.
I checked their permissions.
I renamed the files but they were not created again.

I created a new cluster and it started.
So I guess there's some corruption in the data files.

I replaced the data files with an old copy from 12 hours before but the
server won't start.

I tried to use pg_resetxlog:
# su postgres -c '/usr/lib/postgresql/9.1/bin/pg_resetxlog
/var/lib/postgresql/9.1/main'
The database server was not shut down cleanly.
Resetting the transaction log might cause data to be lost.
If you want to proceed anyway, use -f to force reset.

Then:
# su postgres -c '/usr/lib/postgresql/9.1/bin/pg_resetxlog -f
/var/lib/postgresql/9.1/main'
Transaction log reset

But it still won't start.

What can I do?

Thanks in advance.